| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© 2006 Society of Systematic Biologists
That Awkward Age for Butterflies: Insights from the Age of the Butterfly Subfamily Nymphalinae (Lepidoptera: Nymphalidae)
Edited by Karl Kjer: Associate EditorDepartment of Zoology, Stockholm University Stockholm, 106 91, Sweden E-mail: niklas.wahlberg{at}zoologi.su.se
 |
Abstract |
|---|
 TopNotes Abstract Material and MethodsResultsDiscussionReferences |
|---|
The study of the historical biogeography of butterflies has been hampered by a lack of well-resolved phylogenies and a good estimate of the temporal span over which butterflies have evolved. Recently there has been surge of phylogenetic hypotheses for various butterfly groups, but estimating ages of divergence is still in its infancy for this group of insects. The main problem has been the sparse fossil record for butterflies. In this study I have used a surprisingly good fossil record for the subfamily Nymphalinae (Lepidoptera: Nymphalidae) to estimate the ages of diversification of major lineages using Bayesian relaxed clock methods. I have investigated the effects of varying priors on posterior estimates in the analyses. For this data set, it is clear that the prior of the rate of molecular evolution at the ingroup node had the largest effect on the results. Taking this into account, I have been able to arrive at a plausible history of lineage splits, which appears to be correlated with known paleogeological events. The subfamily appears to have diversified soon after the K/T event about 65 million years ago. Several splits are coincident with major paleogeological events, such as the connection of the African and Asian continents about 21 million years ago and the presence of a peninsula of land connecting the current Greater Antilles to the South American continent 35 to 33 million years ago. My results suggest that the age of Nymphalidae is older than the 70 million years speculated to be the age of butterflies as a whole.
Keywords: Bayesian relaxed clock; Lepidoptera; Nymphalidae; tertiary; timing divergences
Received November 14, 2005; Revised January 23, 2006; Accepted March 28, 2006
Butterflies (Papilionoidea) are one of the best known groups of insects (Boggs et al., 2003), yet their evolutionary history is still shrouded in mystery (Vane Wright, 2003). Only recently have robust phylogenetic hypotheses been published, many of these relying on molecular data (Sperling, 2003). This newfound understanding of relationships among the major lineages of butterflies promises to shed light on the evolutionary history of present-day characters. Fundamental to our understanding of why butterflies are what they are today is when and where important divergence events have happened. However, the historical biogeography of butterflies remains unknown, with advocates of both vicariance and dispersal disagreeing on the order of historical events (de Jong, 2003; Viloria, 2003; Hall et al., 2004; Braby et al., 2005).
The major impediment to resolving the conflict has been a lack of a good estimate of the age of butterflies. The handful of fossils that are available suggest that butterflies are relatively young, with the oldest fossil dated at 48 My (million years) belonging to the family Papilionidae (Durden and Rose, 1978). However, several researchers are convinced that present-day distributions of subfamilies, tribes, and even species are indicative of a strong Gondwanan effect (Miller and Miller, 1997; Viloria, 2003; Braby et al., 2005) and there are suggestions that the age of butterflies is much older, up to 140 My (Shields, 1976; Viloria, 2003). Because all butterflies, and indeed most Lepidoptera, are highly specialized feeders of angiosperm plants as larvae, the age of butterflies cannot predate the origin of angiosperms (unless one is willing to invoke mass colonization of plants once they appeared). Indeed, the patterns of butterfly–plant interactions are phylogenetically conserved, with related species of butterflies feeding on related species of plants (Ehrlich and Raven, 1964; Janz and Nylin, 1998). Current best estimates of angiosperm age range around 180 to 140 My (Wickström et al., 2001; Sanderson et al., 2004; Bell et al., 2005). Most of the orders of plants that are used by butterflies originate around 120 to 60 My. Thus it is safe to say that the maximum possible age of butterflies is 180 to 140 My. However, whether the butterflies are 140 My old (Shields, 1976) or 70 My old (Vane-Wright, 2004) has a huge impact on the possible biogeographical history of the group.
Most estimates of the age of butterflies (reviewed in Braby et al., 2005), or various groups within butterflies, have not been based on phylogenetic hypotheses derived from data, much less on rigorous analyses aimed at estimating dates of divergence using paleobiological approaches or molecular clock analyses. However, several recent studies have been published which have used explicit phylogenetic hypotheses and/or molecular data to estimate ages of divergence. One study reviews existing phylogenetic knowledge of various butterfly groups to ask whether there is a Gondwanan signature in the distributions of sister taxa (de Jong, 2003). The conclusion is that only one pair of sister taxa possibly shows such a signature, with one species found in Australia and the other in South America. Two studies on papilionid species used explicit phylogenetic hypotheses, molecular data, and age constraints based on hypothesized biogeographical events to arrive at an age of 65 to 55 My for origin of the genus Papilio (Zakharov et al., 2004) and an age of about 90 My for the origin of the tribe Troidini (Braby et al., 2005). A third study used an explicit phylogenetic hypothesis of South American satyrine butterflies (Nymphalidae) to suggest that butterflies as a whole probably predate the origin of angiosperm plants (Viloria, 2003). A fourth recent study on the family Pieridae used four fossils to calibrate ages of divergence based on molecular data and came to the conclusion that the family originated some 100 My ago (Mya) (Braby et al., 2006).
The lack of fossils for almost all butterfly groups is a great impediment to getting independent age estimates of various higher taxa when one is interested in explicitly testing historical biogeographic scenarios. The studies by Zakharov et al. (2004) and Braby et al. (2005) used biogeographical scenarios to constrain the ages of several nodes in the phylogeny and so their results cannot be seen as independent tests of biogeographical hypotheses (de Jong, 2003). Thus the jury is still out on the question of how much present-day butterfly distributions have been affected by tectonic events of Gondwanan age, although the recent study by Braby et al. (2006) suggests that deeper divergences in butterflies have been affected significantly.
One group of butterflies that have contributed to the debate on age and history is the family Nymphalidae, which includes butterflies such as the monarch, the blue morphos, and the fritillaries. The phylogenetic relationships of taxa in Nymphalidae have recently been under close scrutiny at both the molecular (Brower, 2000; Wahlberg et al., 2003) and morphological (Freitas and Brown, 2004) levels. The subfamily Nymphalinae has been studied in particular detail (Wahlberg and Zimmermann, 2000; Nylin et al., 2001; Willmott et al., 2001; Wahlberg and Nylin, 2003; Wahlberg et al., 2005), and our understanding of the relationships of the major clades within the subfamily are quite robust. Species belonging to the subfamily, such as checkerspots (Euphydryas and Melitaea), buckeyes (Junonia), and admirals and relatives (Vanessa and Polygonia), have been used as model organisms in ecological and evolutionary studies.
The subfamily Nymphalinae is unique in its family Nymphalidae in that there are five fossils that can be assigned to the subfamily. Three of these are found in the Florissant formation in Colorado, which was formed in the early Oligocene and are thought to be about 34 My in age (Evanoff et al., 2001). One of the fossils, 
Vanessa amerindica, has been placed in the extant genus Vanessa, whereas the other two, Prodryas persephone and Lithopsyche styx, are thought to be related to the extant genus Hypanartia (Emmel et al., 1992). As Vanessa and Hypanartia are putatively sister groups (Wahlberg et al., 2005), the fossils suggest that both lineages had diverged by 34 My. The fourth fossil is a hind wing that has been assigned to the extant genus Aglais, possibly related to the extant species Aglais urticae (Nekrutenko, 1965). The fossil was found in the Karagan deposits from the Miocene and has been dated at 14 My. The fifth fossil is a larva in Dominican amber possibly related to Smyrna (Hammond and Poinar, 1998). The age of this fossil is not entirely clear, but is possibly about 15 to 25 My (Iturralde-Vinent and MacPhee, 1996). Grimaldi and Engel (2005) list several more fossils as being placed in Nymphalinae. However, the classification used here is based on Wahlberg et al. (2003, 2005), which places these fossils in other subfamilies.
In this paper I have used the recent phylogenetic hypothesis for Nymphalinae (Wahlberg et al., 2005) in conjunction with information from fossils to estimate the ages of various major clades. I conclude that the age of Nymphalinae is similar to previous speculations on the age of butterflies as a whole, thus making the butterflies older than generally accepted.
|
Material and Methods |
|---|
|
TopNotesAbstractMaterial and MethodsResultsDiscussionReferences |
|---|
The Data Set
The data set for this study is taken from Wahlberg et al. (2005), which consists of sequence data from three gene regions, the mitochondrial cytochrome oxidase subunit I (1450 bp), the nuclear elongation factor-1
(1077 bp) and wingless (ca. 400 bp), for a total of 2927 base pairs. The main aim of this study is to estimate divergence dates for deeper nodes in the subfamily Nymphalinae; thus, due to computational constraints, 55 exemplar species representing 44 genera were chosen for analysis. For genera represented by two species in the current data set, the species were chosen such that the basal-most split in the genus according to Wahlberg et al. (2005) was preserved. The phylogenetic relationships of the exemplars were taken from Wahlberg et al. (2005) (Fig. 1a). This tree will be referred to as the "parsimony topology." Four outgroup taxa were included in the estimation of branch lengths: Amnosia decora (tribe Pseudergolini), Cyrestis thyodamas (tribe Cyrestini), Historis odius, and Baeotus deucalion (both in the tribe Coeini). These taxa belong to the nymphaline clade of Wahlberg et al. (2003) and may represent the sister taxa of Nymphalinae (which is still uncertain; see Wahlberg et al., 2005). The tree was rooted with Amnosia.
|
Many of the basal nodes are weakly supported and unstable to changes in assumptions of analysis, mainly due to short branch lengths (Wahlberg et al., 2005). To investigate the effects of an alternative topology on estimated times of divergence, the 59-taxon data set described above was subjected to a Bayesian phylogenetic analysis. A GTR+I+
model was applied to each gene partition separately in a combined analysis using the program MrBayes 3.1 (Ronquist and Huelsenbeck, 2003). Two simultaneous runs were allowed to go for 1 million generations and the MCMC chain was sampled every hundredth generation. Each run had four chains, one cold and three heated. To calculate posterior probabilities of clades, the first 1000 sampled generations from each run were discarded as "burn-in" (inspection of log likelihood values showed that equilibrium had been reached by this generation). The maximum a posteriori tree (the tree with the highest likelihood) was used for estimating dates of divergence as detailed below. This tree will be referred to as the "Bayesian topology." The combined data matrix is available from TREEBASE (www.treebase.org, accession number SN2814). Names of clades are taken from Wahlberg et al. (2005).
Estimating Divergence Times
The problem of disentangling times from evolutionary rates in studies on molecular evolution is well known (Gillespie, 1991). Currently it is acknowledged that a clock-like rate of evolution is highly unlikely and that rates of evolution can be lineage specific and indeed temporally specific as well (see, e.g., Gillespie, 1991; Sanderson et al., 2004). Methods that try to take this into account when estimating times of divergence can be nonparametric (or semiparametric) (Sanderson, 1997, 2002) or highly parametric (Kishino et al., 2001; Thorne and Kishino, 2002). The advantages and disadvantages of both methods are discussed by Sanderson et al. (2004). In this study, the Bayesian relaxed clock method (Thorne and Kishino, 2002) was used to estimate times of divergence, as this allows separate models of molecular evolution to be applied to different genes in a simultaneous analysis.
Divergence time estimates using the Bayesian relaxed clock were calculated using the program MULTIDIVTIME (available from J. Thorne, North Carolina State University), which implements a stochastic model for evolutionary rate changes over time (Kishino et al., 2001; Thorne and Kishino, 2002). Branch lengths were estimated separately for each gene on the given topology using the program ESTBRANCHES (part of the MULTIDIVTIME package) after estimating parameter values for the F84 model using PAML (Yang, 1997). In both topologies, the age of the split between the two Vanessa species was constrained to be no older than 34 My, as was the split between the two Hypanartia species. In the parsimony topology, the split between Vanessa and Hypanartia was constrained to be no younger than 34 My. In the Bayesian topology, the split between Vanessa and the Nymphalis-group clade was constrained to be no younger than 34 My. Thus the fossils related to Vanessa and Hypanartia are assumed to represent extinct stem lineages.
In Bayesian analyses of times of divergence, the priors are very important (Thorne and Kishino, 2002; Wiegmann et al., 2003; Sanderson et al., 2004). The three priors that must be defined for the program MULTIDIVTIME are the age of the root, the rates of molecular evolution, and the variation in rates of molecular evolution over time. To investigate the robustness of results to these different priors, a number of combinations of prior values were assessed. The prior distribution for the time separating the ingroup node from the present (±SD) was set to 100 (±80) and 40 (±30) My. These values were chosen based on fossil evidence (the clade of interest cannot be younger than 34 My) and on the assumption that the order Lepidoptera diversified in concert with angiosperm plants (the subfamily Nymphalinae should thus be younger than the origin of angiosperm plants about 140 Mya).
A rough prior for the rate of molecular evolution can be calculated using branch lengths and the prior for the age of the ingroup node (Wiegmann et al., 2003). Branch lengths were estimated using maximum likelihood and a GTR+I+ model of sequence evolution on the fixed parsimony topology using the program PAUP* (Swofford, 2001) for the combined molecular data set. The branch lengths from root to all tips had a median of about 0.15 substitutions per site, translating to a prior of between 0.0015 and 0.003 substitutions per site per My (depending on the prior of the age of the ingroup node). A prior of 0.002 (±0.0015) was thus chosen for analyses. In addition, two other priors for the rate of molecular evolution at the ingroup root node were tested: 0.0002 (±0.00015), and 0.02 (±0.015). The parameter "brownmean" (which affects the variation of rates of molecular evolution over time) was set to 0.002 (±0.002) and 0.02 (±0.02) as in Wiegmann et al. (2003). The prior distributions were purposefully made vague as little is known about the age or rate of molecular evolution in Nymphalinae. All prior distributions were tested on both topologies. Actual values input into the program were adjusted so that one time unit equals 10 My, as J. Thorne advises in the program documentation that the program achieves convergence of the Markov chain best when the prior for the time separating the ingroup node from the present is between 0.1 and 10 units.
As in Wiegmann et al. (2003), initial parameter values were randomly selected to initialize the Markov chain, and then a burn-in period of 100,000 cycles of proposed changes to the current state of the Markov chain was completed before parameters were sampled from the chain. After the burn-in period, the Markov chain was run for 1,000,000 cycles with every 100 cycles sampled. Prior and posterior distributions were approximated based upon the 10,000 samples.
|
Results |
|---|
|
TopNotesAbstractMaterial and MethodsResultsDiscussionReferences |
|---|
Bayesian Phylogenetic Analysis
The Bayesian phylogenetic analysis gave a phylogenetic hypothesis that was very similar to the previous parsimony analysis (Fig. 1). The major differences were in the Nymphalini clade, where Smyrna is found to be sister to Colobura + Tigridia, and importantly Hypanartia is not found to be sister to Vanessa. The Bayesian topology suggests that Vanessa is sister to the Nymphalis-group with strong posterior probability, and that Hypanartia is sister to the latter clade + Antanartia. Such a topology has strong implications on the historical biogeography of the clade, as discussed below. The relationships in the other major clade are similar to the parsimony tree, with differences being concentrated on the relationships of the clades with very short branches at the base of the clade.
Effects of Priors on Divergence Time Estimates
The most recent common ancestor of the subfamily Nymphalinae is estimated to have existed between 105 and 60 Mya, depending on mainly one prior, the prior of the rate of molecular evolution at the ingroup node (Table 1). Increasing the prior decreased the estimated ages of divergences dramatically. Increasing the brownmean prior decreased the estimated ages of divergences much less. The estimated ages of divergence varied more and had broader confidence intervals at the base of the phylogeny than at the more derived nodes. The prior for the time separating the ingroup node from the present did not have a large effect on estimated times of divergence, with the age of the first split in Nymphalinae shown in Table 1 (node 16 in Fig. 1) being decreased to between 90 and 58 My when a prior of 40 My was used, depending on the other priors (see online appendix at http://systematicbiology.org). The different topologies did not have a strong effect on the estimated ages of divergence, with the Bayesian topology consistently giving slightly younger age estimates.
|
The average posterior rate of molecular evolution throughout the whole tree was an order of magnitude greater for the mitochondrial gene COI, compared to the two nuclear genes EF-1
and wingless, regardless of tree topology or priors (Table 2). The parameter describing the variation in the rate of molecular evolution ("brownmean") had a variable posterior value that depended on the priors used, particularly the prior for the rate of molecular evolution (Table 3).
|
|
The large variation in estimates of times of divergence (Table 1) are thus mainly due to the prior describing the rate of molecular evolution. Of the tested rate priors, the two fastest (0.02 and 0.002 substitutions per site per million years) gave similar results, whereas the slowest prior (0.0002 substitutions per site per million years) gave much older estimates. The very rough estimate of rate of molecular evolution based on ML branch lengths and the prior of the age of the ingroup node was of the order of 0.001, whereas the posterior estimates of rates were on the order of 0.01 for COI and 0.001 for EF-1
and wingless (Table 2). Thus, the slow prior is likely to overestimate the ages of divergences. I will base my discussion of the results of the times of divergences estimated with rate priors of 0.02 and 0.002 (the first four columns of Table 1).
Ages of Diversification in Nymphalini
The lineage leading to the present-day Nymphalini (node 15 in Fig. 1) diverged first in the Paleocene or the early Eocene, when the ancestors of Colobura, Tigridia and Smyrna branched off from the stem Nymphalini lineage (Figs. 2 and 3). These three genera are currently very species poor (a total of 5 species) and are restricted to the Neotropics, where they can be common in rainforest habitats. Several important divergences of Nymphalini lineages have happened in the Eocene (53 to 34 Mya). These are the lineages leading to Antanartia, the Symbrenthia clade, the Nymphalis-group clade, the Vanessa clade, and the Hypanartia clade.
|
|
The three genera in the Symbrenthia clade (Symbrenthia, Mynes, and Araschnia) diverged from each other relatively quickly (within a few My), perhaps accounting for the conflicting relationships of these genera in various studies (Nylin et al., 2001; Wahlberg and Nylin, 2003; Fric et al., 2004; Wahlberg et al., 2005). The three genera appear thus to have had a very long period of independent evolution (Figs. 2 and 3).
The two species of Antanartia have diverged from their common ancestor very recently in the Pliocene (Figs. 2 and 3). However, Wahlberg et al. (2005) were unable to sample the three other species of Antanartia; thus, the divergences in this genus may not be representative of the age of the genus.
The Nymphalis- group (including the genera Nymphalis, Polygonia and Aglais; see Wahlberg and Nylin, 2003) diverged from its sister group (Vanessa + Hypanartia or simply Vanessa) in the middle Eocene, but the genera in the clade diversified some 10 My later in the early Oligocene (Figs. 2 and 3). The age of the genus Aglais is consistent with the fossil Aglais from the middle Miocene.
The times of divergences in the genera Vanessa and Hypanartia are of course tied to the constraints imposed by the fossils in the analyses. There is thus very little variation in the estimated ages of the genera in the analyses with the different priors. The two genera are estimated to have diversified in the early Oligocene.
Ages of Diversification in the Kallimoid Clade
The most recent common ancestor of the extant species in the kallimoid clade (node 9, Fig. 1) diverged in the late Paleocene/early Eocene, some 10 My after the divergence of the Nymphalini and kallimoid lineages (Figs. 2 and 3). The basal relationships of the kallimoid clade are poorly supported (Wahlberg et al., 2005) and thus any inferences of ages of divergences must be viewed with caution. However, regardless of topology, several major lineages diverged in early to mid-Eocene. These are Victorinini, Junoniini, Kallimini, Melitaeini, and the rogue taxa Rhinopalpa, Vanessula, and Kallimoides. The rogue taxa (as termed by Wahlberg et al., 2005) have long branches and their phylogenetic positions are very unstable within the kallimoid clade (Wahlberg et al., 2005). The three genera are monotypic and thus further sampling of extant species is not possible. It is clear that these taxa have had a long period of independent evolution, and whether they are remnants of once diverse clades is a matter of speculation.
Victorinini (node 8, Fig. 1) diverged into three lineages in the late Eocene, with two of the lineages diverging further in the late Oligocene/early Miocene (Figs. 2 and 3). The estimated times of divergence for the genus Anartia are much older than previously calculated (Blum et al., 2003), demonstrating the dangers of applying a "standard" molecular clock rate to pairwise sequence divergences.
The lineage leading to Junoniini (node 7, Fig. 1) has had a relatively long period (10 to 15 My) of independent evolution before diverging into the extant genera. There appear to have been two periods of divergences in Junoniini, once in the early to mid-Oligocene and a second time in the early Miocene (Figs. 2 and 3).
Genera in Kallimini have diverged in a steady stream every 7 to 10 My (Figs. 2 and 3). The Australasian Doleschallia is the first to diverge in the mid to late Eocene, then the Asian Kallima in the early Oligocene, and finally the two African genera diverged in the early Miocene.
The lineage leading to Melitaeini has also had a long period of independent evolution (about 10 My) before the current subtribes diverged in the late Eocene and the early Oligocene (Figs. 2 and 3). The subtribes Melitaeina, Phyciodina, and the as yet formally unnamed Chlosyne-group and Gnathotriche-group (see Wahlberg et al., 2005) diverged in quick succession from each other, once again perhaps explaining the difficulty of resolving their relationships (Kons, 2000; Wahlberg and Zimmermann, 2000; Wahlberg et al., 2005). It appears that the unresolved relationships are due to few informative characters rather than character conflict. The subtribes Melitaeina and Phyciodina have diversified during the Miocene.
|
Discussion |
|---|
|
TopNotesAbstractMaterial and MethodsResultsDiscussionReferences |
|---|
Robustness of Estimates
Estimating ages of diversification from molecular and fossil data is still fraught with uncertainties in methodology (Grauer and Martin, 2004; Magallón, 2004; Zaragüeta Bagils et al., 2004; Heads, 2005), although there have been significant recent advances (Sanderson, 2002; Thorne and Kishino, 2002). As in all model-based work, it is of utmost importance to investigate the robustness of one's results to varying parameter values. In this study I have particularly investigated the effect of varying priors in a Bayesian relaxed clock analysis. I have found that for the current data set and associated fossil calibration points, the parameter that affects the results the most is the rate of molecular evolution from the ingroup node. Priors for this parameter which were tested varied threefold and results from the fastest two priors were more similar to each other than to the slowest prior tested (Table 1). This is mainly due to there being no constraint on the age of the root node, allowing the estimated age of the root to stretch further back in time when a slow prior of rate of molecular evolution is invoked (in this case 0.0002 substitutions per site per million years). In contrast, in this study the fossil constraints do not allow the age of the root to come too much forward in time and thus priors that invoke a molecular rate of evolution that is too fast (in this case 0.02 substitutions per site per million years) will not affect the results significantly.
The results are not very sensitive to the other priors used, such as the variation in the rate of evolution, age of the root node, or the phylogenetic hypothesis. However, in initial trials, I used the 50% majority-rule consensus topology from the Bayesian analyses, which had several polytomies (branches with no posterior probabilities in Fig. 1b were collapsed). This topology gave divergence time estimates of the basal splits that were much more recent and with confidence intervals that were narrower than with the fully resolved topology for the same prior combinations used here (see online appendix at http://systematicbiology.org). The effects of polytomies on results of divergence time analyses have not been investigated in detail as yet.
The estimates of times of divergence are heavily dependent on the fossil constraints imposed and thus a critical look at the position of the constraints on the phylogenetic hypotheses is needed. The fossil Vanessa amerindica is thought to be closely related to the extant Vanessa indica (Emmel et al., 1992). However, according to Wahlberg et al. (2005), the clade to which V. indica belongs is clearly of Palaearctic origin, whereas the most recent common ancestor of the genus Vanessa seems to have been present in both the Nearctic and the Palaearctic. Thus it is justified to assume that the fossil Vanessa represents a species that is sister to the extant Vanessa species.
The two other fossils were used to constrain the age of Hypanartia. Both of these are from the Florissant formation in Colorado. Extant Hypanartia are restricted to tropical areas, mainly in South America, with one species reaching the southern border of the United States and three additional species occurring in Mexico. The sister group of Hypanartia is still not clear (as shown in this study), and therefore the distribution of the ancestor of the genus is not clear (also shown in Wahlberg et al. 2005); furthermore, whether an ancestral species colonized South America from North America, or the other way around, is also not clear. The fossils of Prodryas and Lithopsyche do show that an ancestral species of Hypanartia was present in North America some 34 Mya. In either case, it does appear justified to use the fossils to constrain the maximum age of the genus Hypanartia.
General Patterns
Evidently the major evolutionary events in Nymphalinae have happened during the Tertiary (Figs. 2 and 3). The divergence of the two major clades (Nymphalini and the kallimoid clade) coincides with the K/T boundary (the transition from the Cretaceous period to the Tertiary period, about 65 Mya). The K/T boundary is well known for being the point in time when dinosaurs went extinct, perhaps due to the impact of an asteroid. The influence of the K/T event on the extinction rates in herbivorous insects is not well known (Grimaldi and Engel, 2005). One study shows that specialized associations of insects with plants all but disappeared at the K/T boundary and took over 10 My to recover, suggesting that there was a great extinction event in herbivorous insects in the late Cretaceous (Labandeira et al., 2002). Based on fossil evidence, the Tertiary was a period of intense diversification, especially in herbivorous insects (Rasnitsyn and Quicke, 2002). In Nymphalinae, diversification of lineages has happened during the Eocene, Oligocene, and especially the Miocene (at the species level), in line with the observations of Labandeira et al. (2002).
Geologically, the Tertiary is characterized by the final breakup of remnant Gondwana (52 to 30 Mya), the docking of the Indian subcontinent to the Asian continent and subsequent rise of the Himalayas (50 Mya), the connecting of Africa with Europe (60 Mya), the connecting of Africa with Asia (21 Mya), and the connecting of North America with South America (3 Mya) (Scotese et al., 1988; Iturralde-Vinent and MacPhee, 1999; McLoughlin, 2001; Willis and McElwain, 2002; Sanmartín and Ronquist, 2004; Zhu et al., 2005). There also appears to have been an island arc allowing faunistic movements between North America and South America briefly 35 to 33 Mya (Iturralde-Vinent and MacPhee, 1999). These geological events have had an effect on the historical biogeography of Nymphalinae.
The Age of Nymphalinae and Its Biogeography
The historical biogeography of Nymphalinae was investigated by Wahlberg et al. (2005) in detail using dispersal-vicariance analyses (Ronquist, 1997). The most recent common ancestor of Nymphalinae was inferred to have been widespread, although for several clades single continents were found to have been important for the diversification of the subfamily. The ancestral distribution of the tribe Nymphalini was inferred to have been South America, whereas Africa was found to have played an important role in the diversification of the kallimoid clade. The dispersal-vicariance analyses of Wahlberg et al. (2005) are reinterpreted here based on the current results.
The age of Nymphalinae suggests that the primary breakup of Gondwana (i.e., the splitting of Africa from Gondwana some 100 Mya) did not have an effect on the current distributions of species in the subfamily. This is a particularly important observation, as many of the basal divergences in the clade lead to lineages that are predominantly South American (e.g., Smyrna, Colobura, Tigridia, and Victorinini) or African (e.g., Antanartia, Kallimoides, Vanessula, and Junoniini). Because the splitting of Africa from Gondwana happened earlier than the estimated age of the basal divergences, the presence of these lineages on the two continents must be the result of dispersal events between South America and Africa. Which of the two continents was the origin of the dispersalists might be inferred from the distribution of the sister group of Nymphalinae. Of the possible sister groups (Wahlberg et al., 2005), Biblidinae and Coeini are restricted to or mainly restricted to South America, whereas the other potential sister groups (Apaturinae and Cyrestinae) are mainly distributed in Asia, with some genera present in South America. Thus, South America is a likely candidate for the ancestral home of Nymphalinae.
The distribution of the most recent common ancestor of Nymphalinae becomes even more interesting when looking at the Bayesian topology (Figs. 1b and 3). The topology and ages of divergences suggest that ancestors of Nymphalinae genera were widespread in remnant Gondwana (South America, Antarctica, and Australia) in the Paleocene and Eocene. These ancestors have subsequently evolved into present day Smyrna, Colobura, Tigridia, Hypanartia, Victorinini, Mynes, and Doleschallia (the latter two genera being largely restricted to tropical Australasia). This scenario implies a colonization of Africa by the ancestors of Antanartia, Kallimoides + Vanessula, and Junoniini in the mid Eocene (i.e., at least three separate colonization events). There are no known geological events that may have helped the movements of butterflies from South America to Africa some 50 to 40 Mya, and so the colonizations would have been the result of long-distance dispersal events.
There are several instances of sister-group relationships between African and tropical Asian groups that date to the late Oligocene/early Miocene. These are in the tribe Junoniini (Protogoniomorpha + Yoma, Hypolimnas species, and Junonia species, see Wahlberg et al., 2005) and Kallimini: ((Mallika + Catacroptera) Kallima). In Junoniini the direction of colonization appears to have been from Africa to Asia, whereas in Kallimini it is the opposite. All these butterflies are tropical and do not occur in temperate areas. Movements between tropical Asia and Africa at about 25 to 15 Mya ago coincides with the final connection of Arabia with Asia about 21 Mya (Willis and McElwain, 2002).
The biogeography and estimated ages of divergence in the tribe Melitaeini provide some of the strongest evidence for the accuracy of the analyses presented here. Although the place of origin of the lineage leading to Melitaeini is not clear, the most recent common ancestor of the tribe was evidently present in North America (Wahlberg and Zimmermann, 2000; Wahlberg et al., 2005). South America was colonized at least twice from North America, once in the Chlosyne-group and once by the ancestor of Phyciodina and the Gnathotriche-group. The main area of distribution of the Chlosyne-group is North America and tropical Central America, and there are very few species that make it into South America (Wahlberg and Zimmermann, 2000; Wahlberg et al., 2005). It seems clear that South America was colonized recently by species of the Chlosyne-group, perhaps in the past 3 My, after the formation of the Panamanian isthmus.
The Gnathotriche-group + Phyciodina, on the other hand, is almost exclusively South American, and their ancestor is estimated to have existed in the early Oligocene (Table 1, Figs. 2 and 3). This coincides precisely with a geologically short period of time when there apparently was a connection between North and South America through a peninsula (or series of islands with short gaps between them) stretching from northern South America almost to the Yucatan peninsula in Central America (known as GAARlandia; Iturralde-Vinent and MacPhee, 1999). The connection was above sea level between 35 to 33 Mya, well within the confidence limits of the age of diversification of the Gnathotriche-group + Phyciodina. Thus it would appear that the ancestral species colonized South America and then diversified into the high-altitude Andean Gnathotriche-group (with 4 species) and the lower altitude Phyciodina.
Other genera that were possibly affected by GAARlandia are Hypanartia, Smyrna, and Anartia. Hypanartia is made up of two distinct clades, one of which is entirely restricted to Andean regions of northern South America and the other is more widespread in lowlands of South America, Central America, and most importantly with an endemic species on the Greater Antilles (Willmott et al., 2001). The Caribbean species is sister to the rest of the species in the latter clade. The fossils in North America and the estimated age of divergence of the two clades coincides with the possible existence of GAARlandia, although the direction of colonization is not clear. According to the Bayesian topology (Fig. 3), the most plausible scenario is for the ancestor of the Hypanartia lethe-clade to have colonized North America from South America. According to the parsimony topology (Fig. 2), the opposite would be more plausible. The possible fossil larva of Smyrna from Dominican amber (Hammond and Poinar, 1998) suggests that Smyrna was present in the Greater Antilles, although it does not occur there currently. The age of the amber suggests that Smyrna was present in GAARlandia.
Two species of Anartia, not sampled by Wahlberg et al. (2005), are endemic to the Greater Antilles. These two species are sister to each other and are the sister group to the other three species of Anartia (Blum et al., 2003). Given that the age of the three Anartia species sampled in my study is much older than thought, with the split between A. jatrophae and the other two species going back to the early Miocene, it is conceivable that the two Caribbean species are remnants of a widespread species that was found in GAARlandia some 34 Mya.
Clearly the study of the historical biogeography of Nymphalinae will benefit from species-level phylogenies. Such phylogenies will give us more understanding of the biogeography of the ancestral species, which will in turn help us refine our estimates of divergence times in these butterflies.
An Awkward Age?
Vane-Wright (2004) highlighted that our knowledge of the age of butterflies is going through a period of "adolescence" (hence the title of his commentary, taken from the novel The Awkward Age by Henry James; R. I. Vane-Wright, personal communication), and that future studies would help us get more insight into how long butterflies have existed. The results presented here cast some light on the age of butterflies, if only indirectly. It appears that the ancestor of Nymphalinae was present before the K/T boundary and diversified after the great extinction event associated with the shift from the Cretaceous to the Tertiary. If this is truly so, the age of the family Nymphalidae must be substantially older than the 70 My proposed as the age of all butterflies (Vane-Wright, 2004). My results suggest an intriguing new hypothesis for Nymphalidae: the family initially diverged prior to the K/T event and of the initial divergences, 12 lineages currently considered to be subfamilies of Nymphalidae survived the K/T event and subsequently diverged in the Tertiary. Other lineages may also have survived, but we have no fossil evidence of such extinct lineages. To test this hypothesis, one would have to investigate whether diversifications of the other subfamilies happened at the same relative time as the diversification of Nymphalinae.
The effect of the K/T event on butterflies has not been investigated in detail, largely because it has not been possible to associate the time of the event with any evolutionary events in butterflies (e.g., diversifications). The genus Papilio is thought to have diversified after the K/T event 65 to 55 Mya (Zakharov et al., 2004), as is the diversification of the main genera of the papilionid tribe Troidini (Braby et al., 2005). This implies that the K/T event has had an important effect on the diversification of various clades in butterflies. Further studies on other clades in butterflies will corroborate or reject this hypothesis. Both of the papilionid studies suggest that the age of butterflies as a whole is much older than 70 My, which is also suggested by my study and the study on Pieridae by Braby et al. (2006). It is obvious that only a thorough study of the butterfly clade would help clear up its age.
|
Acknowledgements |
|---|
This work has been supported by grant number 621-2004-2853 from the Swedish Research Council. I am grateful to Sören Nylin and Chris Wheat for discussions on butterfly evolution, and to Rod Page, Karl Kjer, Felix Sperling, and Simon Ho for critical and useful comments on the previous version of the manuscript.
|
Notes |
|---|
|
TopNotesAbstractMaterial and MethodsResultsDiscussionReferences |
|---|
Current address: Laboratory of Genetics, Department of Biology, University of Turku, 20014, Turku, Finland
|
References |
|---|
|
TopNotesAbstractMaterial and MethodsResultsDiscussionReferences |
|---|
-
Bell C. D., Soltis D. E., Soltis P. S. The age of angiosperms: A molecular timescale without a clock. Evolution (2005) 59:1245–1258.[CrossRef][Web of Science][Medline]
Blum M. J., Bermingham E., Dasmahapatra K. A molecular phylogeny of the neotropical butterfly genus Anartia (Lepidoptera: Nymphalidae). Mol. Phyl. Evol. (2003) 26:46–55.[CrossRef][Web of Science][Medline]
Boggs C. L., Watt W. B., Ehrlich P. R., eds. Butterflies: Evolution and ecology taking flight (2003) Chicago: University of Chicago Press.
Braby M. F., Trueman J. W. H., Eastwood R. When and where did troidine butterflies (Lepidoptera: Papilionidae) evolve? Phylogenetic and biogeographic evidence suggests an origin in remnant Gondwana in the Late Cretaceous. Invertebr. Syst. (2005) 19:113–143.[CrossRef]
Braby M. F., Vila R., Pierce N. E. Molecular phylogeny and systematics of the Pieridae (Lepidoptera: Papilionoidea): Higher classification and biogeography. Zool. J. Linn. Soc. (2006) 147:239–275.[CrossRef]
Brower A. V. Z. Phylogenetic relationships among the Nymphalidae (Lepidoptera), inferred from partial sequences of the wingless gene. Proc. R. Soc. Lond. B (2000) 267:1201–1211.[CrossRef]
de Jong R. Are there butterflies with Gondwanan ancestry in the Australian region? Invertebr. Syst. (2003) 17:143–156.[CrossRef]
Durden C. J., Rose H. Butterflies from the middle Eocene: The earliest occurrence of fossil Papilionidae. Pearce-Sellards Ser. Tex. Mem. Mus. (1978) 29:1–25.
Ehrlich P. R., Raven P. H. Butterflies and plants: A study in coevolution. Evolution (1964) 18:586–608.[CrossRef][Web of Science]
Emmel T. C., Minno M. C., Drummond B. A. Florissant butterflies: A guide to the fossil and present-day species of Central Colorado (1992) Stanford: Stanford University Press.
Evanoff E., McIntosh W. C., Murphey P. C. Stratigraphic summary and 40Ar/39Ar geochronology of the Florissant Formation, Colorado. In: Fossil flora and stratigraphy of the Florissant Formation, Colorado—Evanoff E., Gregory-Wodzicki K. M., Johnson K. R., eds. (2001) Denver, Colorado: Denver Museum of Nature and Science Proceedings. 1–16.
Freitas A. V. L., Brown K. S. J. Phylogeny of the Nymphalidae (Lepidoptera: Papilionoidea). Syst. Biol. (2004) 53:363–383.
Fric Z., Konvicka M., Zrzav
J. Red & black or black & white? Phylogeny of the Araschnia butterflies (Lepidoptera: Nymphalidae) and evolution of seasonal polyphenism. J. Evol. Biol. (2004) 17:265–278.[CrossRef][Web of Science][Medline]
Gillespie J. H. The causes of molecular evolution (1991) Oxford, UK: Oxford University Press.
Grauer D., Martin W. Reading the entrails of chickens: Molecular timescales of evolution and the illusion of precision. TIG (2004) 20:80–86.[Medline]
Grimaldi D., Engel M. S. Evolution of the insects (2005) New York: Cambridge University Press.
Hall J. P. W., Robbins R. K., Harvey D. J. Extinction and biogeography in the Caribbean: new evidence from a fossil riodinid butterfly in Dominican amber. Proc. R. Soc. Lond. B (2004) 271:797–801.[CrossRef][Medline]
Hammond P. C., Poinar G. Jr. A larval brush-footed butterfly (Lepidoptera: Nymphalidae) in Dominican amber, with a summary of fossil Nymphalidae. Ent. scand. (1998) 29:275–279.
Heads M. Dating nodes on molecular phylogenies: A critique of molecular biogeography. Cladistics (2005) 21:62–78.[Web of Science]
Iturralde-Vinent M. A., MacPhee R. D. E. Age and paleogeographic origin of Dominican amber. Science (1996) 273:1850–1852.
Iturralde-Vinent M. A., MacPhee R. D. E. Paleogeography of the Caribbean region: Implications for Cenozoic biogeography. Bull. Am. Mus. Nat. Hist. (1999) 238:1–95.
Janz N., Nylin S. Butterflies and plants: A phylogenetic study. Evolution (1998) 52:486–502.[CrossRef][Web of Science]
Kishino H., Thorne J. L., Bruno W. J. Performance of a divergence time estimation method under a probabilistic model of rate evolution. Mol. Biol. Evol. (2001) 18:352–361.
Kons H. L. J. Phylogenetic studies of the Melitaeini (Lepidoptera: Nymphalidae: Nymphalinae) and a revision of the genus Chlosyne Butler (2000) Gainesville: University of Florida. 799. PhD thesis.
Labandeira C. C., Johnson K. R., Wilf P. Impact of the terminal Cretaceous event on plant-insect associations. Proc. Natl. Acad. Sci. USA (2002) 99:2061–2066.
Magallón S. A. Dating lineages: Molecular and paleontological approaches to the temporal framework of clades. Int. J. Plant Sci. (2004) 165:S7–S21.[CrossRef][Web of Science]
McLoughlin S. The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism. Aust. J. Bot. (2001) 49:271–300.[CrossRef][Web of Science]
Miller L. D., Miller J. Y. Gondwanan butterflies: The Africa-South America connection. Metamorphosis (1997) 3(suppl.):42–51.
Nekrutenko Y. P. Tertiary nymphalid butterflies and some phylogenetic aspects of systematic lepidopterology. J. Res. Lepid. (1965) 4:149–158.
Nylin S., Nyblom K., Ronquist F., Janz N., Belicek J., Källersjö M. Phylogeny of Polygonia, Nymphalis and related butterflies (Lepidoptera: Nymphalidae): A total-evidence analysis. Zool. J. Linn. Soc. (2001) 132:441–468.[CrossRef]
Rasnitsyn A. P., Quicke D. L. J., eds. History of insects (2002) Dordrecht, Germany: Kluwer Academic Publishers.
Ronquist F. Dispersal-vicariance analysis: A new approach to the quantification of historical biogeography. Syst. Biol. (1997) 46:195–203.
Ronquist F., Huelsenbeck J. P. MrBayes 3: Bayesian phylogenetic inference under mixed models. Bioinformatics (2003) 19:1572–1574.
Sanderson M. J. A nonparametric approach to estimating divergence times in the absence of rate constancy. Mol. Biol. Evol. (1997) 14:1218–1231.[Web of Science]
Sanderson M. J. Estimating absolute rates of molecular evolution and divergence times: A penalized likelihood approach. Mol. Biol. Evol. (2002) 19:101–109.
Sanderson M. J., Thorne J. L., Wikström N., Bremer K. Molecular evidence on plant divergence times. Am. J. Bot. (2004) 91:1656–1665.
Sanmartín I., Ronquist F. Southern hemisphere biogeography inferred by event-based models: Plant versus animal patterns. Syst. Biol. (2004) 53:216–243.
Scotese C. R., Gahagan L. M., Larson R. L. Plate tectonic reconstructions of the Cretaceous and Cenozoic ocean basins. Tectonophysics (1988) 155:27–48.[CrossRef][Web of Science]
Shields O. Fossil butterflies and the evolution of Lepidoptera. J. Res. Lepid. (1976) 15:132–143.
Sperling F. A. H. Butterfly species and molecular phylogenies. In: Butterflies: Evolution and ecology taking flight—Boggs C. L., Watt W. B., Ehrlich P. R., eds. (2003) Chicago: University of Chicago Press. 431–458.
Swofford D. L. PAUP*: Phylogenetic analysis using parsimony (* and other methods) (2001) Sunderland, Massachusetts: Sinauer Associates. version 4.0b10.
Thorne J. L., Kishino H. Divergence time and evolutionary rate estimation with multilocus data. Syst. Biol. (2002) 51:689–702.
Vane-Wright R. Butterflies at that awkward age. Nature (2004) 428:477–480.[CrossRef][Medline]
Vane-Wright R. I. Evidence and identity in butterfly systematics. In: Butterflies: Evolution and ecology taking flight—Boggs C. L., Watt W. B., Ehrlich P. R., eds. (2003) Chicago: University of Chicago Press. 477–514.
Viloria A. L. Historical biogeography and the origins of the satyrine butterflies of the Tropical Andes (Insecta: Lepidoptera, Rhopalocera). In: Una perspectiva latinoamericana de la biogeografía México, D. F.—Morrone J. J., Llorente-Bousquets J., eds. (2003) Mexico City, Mexico: Las Prensas de Ciencias, Facultad de Ciencias, UNAM. 247–261.
Wahlberg N., Brower A. V. Z., Nylin S. Phylogenetic relationships and historical biogeography of tribes and genera in the subfamily Nymphalinae (Lepidoptera: Nymphalidae). Biol. J. Linn. Soc. (2005) 86:227–251.[CrossRef][Web of Science]
Wahlberg N., Nylin S. Morphology versus molecules: Resolution of the positions of Nymphalis, Polygonia and related genera (Lepidoptera: Nymphalidae). Cladistics (2003) 19:213–223.[CrossRef][Web of Science]
Wahlberg N., Weingartner E., Nylin S. Towards a better understanding of the higher systematics of Nymphalidae (Lepidoptera: Papilionoidea). Mol. Phyl. Evol. (2003) 28:473–484.[CrossRef][Web of Science][Medline]
Wahlberg N., Zimmermann M. Pattern of phylogenetic relationships among members of the tribe Melitaeini (Lepidoptera: Nymphalidae) inferred from mtDNA sequences. Cladistics (2000) 16:347–363.[CrossRef][Web of Science]
Wickström N., Savolainen V., Chase M. W. Evolution of the angiosperms: Calibrating the family tree. Proc. R. Soc. Lond. B (2001) 268:2211–2220.[Medline]
Wiegmann B., Yeates D., Thorne J. L., Kishino H. Time flies, a new molecular time-scale for brachyceran fly evolution without a clock. Syst. Biol. (2003) 52:745–756.
Willis K. J., McElwain J. C. The evolution of plants (2002) Oxford, UK: Oxford University Press.
Willmott K. R., Hall J. P. W., Lamas G. Systematics of Hypanartia (Lepidoptera: Nymphalidae: Nymphalinae), with a test for geographical speciation mechanisms in the Andes. Syst. Ent. (2001) 26:369–399.[CrossRef]
Yang Z. PAML: A program package for phylogenetic analysis by maximum likelihood. Comput. Appl. Biosci. (1997) 13:555–556.
Zakharov E. V., Caterino M. S., Sperling F. A. H. Molecular phylogeny, historical biogeography and divergence time estimates for swallowtail butterflies of the genus Papilio (Lepidoptera: Papilionidae). Syst. Biol. (2004) 53:193–215.
Zaragüeta Bagils R., Lelièvre H., Tassy P. Temporal paralogy, cladograms, and the quality of the fossil record. Geodiversitas (2004) 26:381–389.[Web of Science]
Zhu B., Kidd W. S. F., Rowley D. B., Currie B. S., Shafique N. Age of initiation of the India-Asia collision in the East-Central Himalaya. J. Geol. (2005) 113:265–285.[CrossRef][Web of Science]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  N. Wahlberg, J. Leneveu, U. Kodandaramaiah, C. Pena, S. Nylin, A. V. L. Freitas, and A. V. Z. Brower Nymphalid butterflies diversify following near demise at the Cretaceous/Tertiary boundary Proc R Soc B, December 22, 2009; 276(1677): 4295 - 4302. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Pena and N. Wahlberg Prehistorical climate change increased diversification of a group of butterflies Biol Lett, June 23, 2008; 4(3): 274 - 278. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Wahlberg and C. W. Wheat Genomic Outposts Serve the Phylogenomic Pioneers: Designing Novel Nuclear Markers for Genomic DNA Extractions of Lepidoptera Syst Biol, April 1, 2008; 57(2): 231 - 242. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Venditti, A. Meade, and M. Pagel Phylogenetic Mixture Models Can Reduce Node-Density Artifacts Syst Biol, April 1, 2008; 57(2): 286 - 293. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||