Systematic Biology最新文献

The total number of species on earth and the rate at which new species are created are fundamental questions for ecology, evolution and conservation. These questions have typically been approached separately, despite their obvious interconnection. In this study, we approach both questions in conjunction, for all terrestrial animals. To do this, we combine two previously unconnected bodies of theory: general ecosystem models and individual-based ecological neutral theory. General ecosystem models provide us with estimated numbers of individual organisms, separated by functional group and body size. Neutral theory, applied within a guild of functionally similar individuals, connects species richness, speciation rate, and number of individual organisms. In combination, for terrestrial endotherms where species numbers are known, they provide us with estimates for speciation rates as a function of body size and diet class. Extrapolating the same rates to guilds of ectotherms enables us to estimate the species richness of those groups, including species yet to be described. We find that speciation rates per species per million years decrease with increasing body size. Rates are also higher for carnivores compared to omnivores or herbivores of the same body size. Our estimate for the total number of terrestrial species of animals is in the range 1.03-2.92 million species, a value consistent with estimates from previous studies, despite having used a fundamentally new approach. Perhaps what is most remarkable about these results is that they have been obtained using only limited data from larger endotherms and their speciation rates, with the predictive process being based on mechanistic theory. This work illustrates the potential of a new approach to classic eco-evolutionary questions, while also adding weight to existing predictions. As we now face an era of dramatic biological change, new methods will be needed to mechanistically model global biodiversity at the species and individual organism level. This will be a huge challenge but the combination of general ecosystem models and neutral theory that we introduce here is a way to tractably achieve it.

-The interplay of key innovation and ecological opportunity is commonly recognized to be the catalyst for rapid radiation. Underground storage organs (USOs), as a vital ecological trait, are advantageous for the adaptation of plants to extreme environments, but receive less attention compared to aboveground organs. Repeated evolution of various USOs has occurred across the plant tree of life. However, whether repeated occurrences of a USO in different clades of a group can promote its replicated radiations in combination with the invasion of similar environments remains poorly known. Corydalis is a megadiverse genus in Papaveraceae and exhibits remarkable variations in USO morphology and biome occupancy. Here, we first generated a robust phylogeny for Corydalis with wide taxonomic and genomic coverage based on plastome and nuclear ribosomal DNA sequence data. By dating the branching events, reconstructing ancestral ranges, evaluating diversification dynamics, and inferring evolutionary patterns of USOs and biomes and their correlations, we then tested whether the interplay of USO evolution and biome shifts has driven rapid diversification of some Corydalis lineages. Our results indicate that Corydalis began to diversify in the Qinghai-Tibet Plateau (QTP) at ca. 41 Ma, and 88% of dispersals happened through forests, suggesting that forests served as important dispersal corridors for range expansion of the genus. The storage root has originated independently at least 6 times in Corydalis since the Miocene, and its acquisition could have operated as a key innovation toward the adaptation to the alpine biome in the QTP. Repeated evolution of this game-changing trait and invasions of alpine biome, in combination with geoclimatic changes, could have jointly driven independent radiations of the 2 clades of Corydalis in the QTP at ca. 6 Ma. Our study provides new insights into the joint contribution of USO repeated evolution and biome shifts to replicated radiations, hence increasing our ability to predict evolutionary trajectories in plants facing similar environmental pressures.

Comparisons of extant and extinct biodiversity are often dependent on objective morphology-based identifications of fossils and assume a well-established and comparable taxonomy for both fossil and modern taxa. However, since many modern (cryptic) species are delimitated mainly via external morphology and/or molecular data, it is often unclear to what degree fossilized (osteological) remains allow classification to a similar level. When intraspecific morphological variation in extant taxa is poorly known, the definition of extinct species as well as the referral of fossils to extant species can be heavily biased, particularly if fossils are represented by incomplete isolated skeletal elements. This problem is especially pronounced in squamates (lizards and snakes) owing to a lack of osteological comparative knowledge for many lower taxonomic groups, concomitant with a recent increase of molecular studies revealing great cryptic diversity. Here, we apply a quantitative approach using 3D geometric morphometrics on 238 individuals of 14 genera of extant Australian and Papua New Guinean agamid lizards to test the value of 2 isolated skull bones (frontals and maxillae) for inferring taxonomic and ecological affinities. We further test for the consistency of intra- and interspecific morphological variability of these elements as a proxy for extinct taxonomic richness. We show that both bones are diagnostic at the generic level, and both can infer microhabitat and are of paleoecological utility. However, species-level diversity is likely underestimated by both elements, with ~30-40% of species pairs showing no significant differences in shape. Mean intraspecific morphological variability is largely consistent across species and bones and thus a useful proxy for extinct species diversity. Reducing sample size and landmark completeness to approximate fossil specimens led to decreased classification accuracy and increased variance of morphological disparity, raising further doubts on the transferability of modern species borders to the fossil record of agamids. Our results highlight the need to establish appropriate levels of morphology-based taxonomic or ecological groupings prior to comparing extant and extinct biodiversity.