Evolutionary developmental biology ("evo-devo") has revolutionized evolutionary biology but has had relatively little impact on systematics. We show that similar large-scale developmental changes in distantly related lineages can dramatically mislead phylogenetic analyses based on morphological data. Salamanders are important model systems in many fields of biology and are of special interest in that many species are paedomorphic and thus never complete metamorphosis. A recent study of higher-level salamander phylogeny placed most paedomorphic families in a single clade based on morphological data. Here, we use new molecular and morphological data to show that this result most likely was caused by the misleading effects of paedomorphosis. We also provide a well-supported estimate of higher-level salamander relationships based on combined molecular and morphological data. Many authors have suggested that paedomorphosis may be problematic in studies of salamander phylogeny, but this hypothesis has never been tested with a rigorous phylogenetic analysis. We find that the misleading effects of paedomorphosis on phylogenetic analysis go beyond the sharing of homoplastic larval traits by paedomorphic adults, and the problem therefore is not solved by simply excluding suspected paedomorphic characters. Instead, two additional factors are critically important in causing paedomorphic species to be phylogenetically "misplaced": (1) the absence of clade-specific synapomorphies that develop during metamorphosis in nonpaedomorphic taxa and allow their "correct" placement and (2) parallel adaptive changes associated with the aquatic habitat of the larval stage. Our results suggest that the effects of paedomorphosis on phylogenetic analyses may be complex, difficult to detect, and can lead to results that are both wrong and statistically well supported by parsimony and Bayesian analyses.

Abstract. The transition from aquatic to terrestrial eggs is a key evolutionary change that has allowed vertebrates to successfully colonize and exploit the land. Although most amphibians retain the primitive biphasic life cycle (eggs deposited in water that hatch into free-living aquatic larvae), direct development of terrestrial eggs has evolved repeatedly and may have been critical to the evolutionary success of several amphibian groups. We provide the first conclusive evidence for evolutionary reversal of direct development in vertebrates. The family Plethodontidae (lungless salamanders) contains the majority of salamander species, including major radiations of direct developers. We reconstruct the higher level phylogenetic relationships of plethodontid salamanders using molecular and morphological data and use this phylogeny to examine the evolution of direct development. We show that the predominantly biphasic desmognathines, previously considered the sister group of other plethodontids, are nested inside a group of directdeveloping species (Plethodontini) and have re-evolved the aquatic larval stage. Rather than being an evolutionary dead end, the reversal from direct developing to biphasic life history may have helped communities in eastern North America to achieve the highest local diversity of salamander species in the world.

Aim  We used inferences of phylogenetic relationships and divergence times for three lineages of highland pitvipers to identify broad‐scale historical events that have shaped the evolutionary history of Middle American highland taxa, and to test previous hypotheses of Neotropical speciation. Location  Middle America (Central America and Mexico). Methods  We used 2306 base pairs of mitochondrial gene sequences from 178 individuals to estimate the phylogeny and divergence times of New World pitviper lineages, focusing on three genera (Atropoides, Bothriechis and Cerrophidion) that are broadly co‐distributed across Middle American highlands. Results  We found strong correspondence across three highland lineages for temporally and geographically coincident divergences in the Miocene and Pliocene, and further identified widespread within‐species divergences across multiple lineages that occurred in the early–middle Pleistocene. Main conclusions  Available data suggest that there were at least three major historical events in Middle America that had broad impacts on species divergence and lineage diversification among highland taxa. In addition, we find widespread within‐species genetic structure that may be attributable to the climatic changes that affected gene flow among highland taxa during the middle–late Pleistocene.

Abstract.-From literature data on 116 taxa crosses involving 46 species of frogs, we found a positive correlation between degree of divergence (measured as Nei's genetic distance, D) and degree of postzygotic isolation. In anurans, hybrid sterility appears to evolve more quickly than inviability, which is consistent with the conclusions of other studies that involved Drosophila species. The lower threshold of D = 0.30 for evolution of hybrid inviability that we found is similar to that observed for Drosophila. This consistency suggests that there may be a general pattern in the acquisition of reproductive isolation in animals.Key words.-Anura, comparative method, frogs, reproductive isolation, speciation.Received February 3, 1998. Accepted August 10, 1998 A variety of approaches have been presented to elucidate the relationship between reproductive isolation (the defining feature of the speciation process according to adherents of the biological species concept) and degree of genetic divergence (e.g., Ayala et al. 1974). Coyne and Orr (1989,1997) have presented the most comprehensive surveys in this area, using data from hybridization between species of Drosophila. They found that strength of both prezygotic and postzygotic isolation barriers are positively correlated with pairwise genetic distance (and thus, presumably, time of divergence) between species. Although Coyne and Orr (1989) could not detect a significant difference between rates of acquisition of hybrid sterility and hybrid inviability, their original test was criticized for lack of statistical power (Wu 1992). Wu and Davis (1993) presented various lines of evidence that strongly suggest that the rate of evolution of hybrid sterility must be much greater than that of hybrid inviability in Drosophila. In their reanalysis, Coyne and Orr (1997) also found a higher rate of evolution of hybrid sterility than hybrid inviability. As Coyne and Orr (1997) pointed out, the data from Drosophila are unique with respect to their quantity and degree of detail and are likely to remain so, due to the great number of species that can hybridize and the ease of measuring preand postzygotic isolation in the laboratory.In plethodontid salamanders of the Desmognathus ochrophaeus complex, Tilley et al. (1990) and Tilley and Mahoney (1996) found that level of behavioral (prezygotic) isolation among populations cannot be predicted simply from genetic distances. Few other studies of which we are aware involved simultaneous investigation of both reproductive isolation and genetic divergence in amphibians. Anurans (frogs) in particular have the potential to yield many insights into the evolution of reproductive isolation because the reproductive biology of some taxa has been studied intensively (reviewed by Duellman and Trueb 1994). In particular, premating isolation mechanisms between closely related species are already documented for several groups (e.g., W. E Blair 1956Blair , 1958aBlair ,b, 1964Blair , 1972Gerhardt 1974;Ryan 1985;Ryan and Rand 1995), and the degree o...

From literature data on 116 taxa crosses involving 46 species of frogs, we found a positive correlation between degree of divergence (measured as Nei's genetic distance, D) and degree of postzygotic isolation. In anurans, hybrid sterility appears to evolve more quickly than inviability, which is consistent with the conclusions of other studies that involved Drosophila species. The lower threshold of D = 0.30 for evolution of hybrid inviability that we found is similar to that observed for Drosophila. This consistency suggests that there may be a general pattern in the acquisition of reproductive isolation in animals.

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