Alan de Queiroz

The usefulness of behavior for phylogeny estimation : levels of homoplasy in behavioral and morphological characters

It is widely believed that behavior is more evolutionarily labile and/or more difficult to characterize than morphology, and thus that behavioral characters are not as useful as morphological characters for estimating phylogenetic relationships. To examine the relative utility of behavior and morphology for estimating phylogeny, we compared levels of homoplasy for morphological and behavioral characters that have been used in systematic studies. In an analysis of 22 data sets that contained both morphological and behavioral characters we found no significant difference between mean consistency indices (CIs, which measure homoplasy) within data sets for the two types of characters. In a second analysis we compared overall CIs for 8 data sets comprised entirely of behavioral characters with overall CIs for 32 morphological data sets and found no significant difference between the two types of data sets. For both analyses, 95% confidence limits on the difference between the two types of characters indicate that, even if given the benefit of the doubt, morphological characters could not have substantially higher mean CIs than behavioral characters. These results do not support the idea that behavioral characters are less useful than morphological characters for the estimation of phylogeny.

THE EVOLUTION OF EMBRYO SIZE IN ANGIOSPERMS AND OTHER SEED PLANTS: IMPLICATIONS FOR THE EVOLUTION OF SEED DORMANCY

Abstract.— Seed dormancy plays an important role in germination ecology and seed plant evolution. Morphological seed dormancy is caused by an underdeveloped embryo that must mature prior to germination. It has been suggested that the presence of an underdeveloped embryo is plesiomorphic among seed plants and that parallel directional change in embryo morphology has occurred separately in gymnosperms and in angiosperms. We test these hypotheses using original data on embryo morphology of key basal taxa, a published dataset, and the generalized least squares (GLS) method of ancestral character state reconstruction. Reconstructions for embryo to seed ratio (E:S) using family means for 179 families showed that E:S has increased between the ancestral angiosperm and almost all extant angiosperm taxa. Species in the rosid clade have particularly large embryos relative to the angiosperm ancestor. Results for the gymnosperms show a similar but smaller increase. There were no statistically significant differences in E:S between basal taxa and any derived group due to extremely large standard errors produced by GLS models. However, differences between reconstructed values for the angiosperm ancestor and more highly nested nodes are large and these results are robust to topological and branch‐length manipulations. Our analysis supports the idea that the underdeveloped embryo is primitive among seed plants and that there has been a directional change in E:S within both angiosperms and gymnosperms. Our analysis suggests that dormancy enforced by an underdeveloped embryo is plesiomorphic among angiosperms and that nondormancy and other dormancy types probably evolved within the angiosperms. The shift in E:S was likely a heterochronic change, and has important implications for the life history of seed plants.

Contingent Predictability in Evolution: Key Traits and Diversification

Key innovations have often been invoked to explain the exceptional diversification of particular groups. However, there are few convincing examples of traits that are repeatedly and consistently associated with increased diversification. The paucity of such cases may reflect the contingent nature of the diversifying effect of key traits. These contingencies can be viewed as statistical interactions between the trait and at least three kinds of factors: (1) other taxa, (2) other traits of the group itself, and (3) the physical environment. I describe tentative examples in each of these categories: (1) a dampening of the diversification of clades with image-forming eyes by groups that earlier evolved such eyes, (2) an effect of growth form (woody or herbaceous) on the diversifying effect of biotic seed dispersal in angiosperms, and (3) an effect of atmospheric CO 2 level on the diversifying effect of C 4 photosynthesis in monocots. These examples suggest the need for more complex analyses of the relationship between possible key traits and diversification. They also suggest that radiations may be predictable given certain circumstances, thus supporting a view of evolution as both predictable and contingent. Ironically, a certain degree of predictability may be critical to arguments for evolutionary contingency.

DO IMAGE-FORMING EYES PROMOTE EVOLUTIONARY DIVERSIFICATION?

It has been suggested that image‐forming eyes promote the evolutionary diversification (measured by species richness) of the groups that possess them. Several different processes could give rise to this effect, including diversifying selection in a new adaptive zone (or zones) and a reduced rate of extinction due to enhanced competitive abilities. I tested the generality of the hypothesis that imaging eyes increase net speciation by comparing extant species numbers of 12 groups that have such eyes (as categorized by Land and Fernald 1992) with those of their cladistic sister groups that lack such organs. Even assuming the published hypotheses of phylogenetic relationships that most favor increased net speciation of visual groups, these comparisons show no significant association between imaging eyes and species richness. Increased activity, as indicated by published accounts of locomotory speed, is significantly associated with the evolution of image‐forming eyes. This suggests that a large “visual adaptive zone” might be characterized by relatively high activity. However, when diversity comparisons are limited to eight cases in which the evolution of imaging eyes is associated with increased activity, there is still no significant association between such eyes and species richness. The fossil record indicates that the only visual groups that have undergone major evolutionary radiations evolved imaging eyes early in the history of metazoans (before the Silurian). The radiations of these early groups may have largely filled up niches for visual animals and thus prevented the subsequent proliferation of other groups with image‐forming eyes. Alternatively, it may be that image‐forming eyes have no exceptional effect on diversification or that their effects are obscured by other factors in the long run.