Miocene biome turnover drove conservative body size evolution across Australian vertebrates

Phylogenetic biome conservatism as a key concept for an integrative understanding of evolutionary history: Galliformes and Falconiformes as study cases

Biomes are climatically and biotically distinctive macroecological units that formed over geological time scales. Their features consolidate them as ‘evolutionary scenarios’, with their own diversification dynamics. Under the concept of phylogenetic niche conservatism, we assessed, for the first time, the evolution of biome occupation in birds. We aimed to analyse patterns of adaptation to different climatic regimes and the determinant factors for colonization of emerging biomes by clades from different ancestral biomes. In this work, we reconstructed the biome occupation history of two clades of birds (Galliformes and Falconiformes) under an integrative perspective through a comprehensive review of ecological, phylogenetic, palaeontological and biogeographical evidence. Our findings for both groups are consistent with a scenario of phylogenetic biome conservatism and highlight the importance of changes in climate during the Miocene in the adaptation and evolution of climatic niches. In particular, our results indicate high biome conservatism associated with biomes situated in some of the extremes of the global climate gradient (evergreen tropical rainforest, steppe and tundra) for both bird taxa. Finally, the historical dynamics of tropical seasonal biomes, such as tropical deciduous woodlands and savannas, appear to have played a preponderant role during the diversification processes of these bird lineages.

Geographic range size and speciation in honeyeaters

BACKGROUND

Darwin and others proposed that a species' geographic range size positively influences speciation likelihood, with the relationship potentially dependent on the mode of speciation and other contributing factors, including geographic setting and species traits. Several alternative proposals for the influence of range size on speciation rate have also been made (e.g. negative or a unimodal relationship with speciation). To examine Darwin's proposal, we use a range of phylogenetic comparative methods, focusing on a large Australasian bird clade, the honeyeaters (Aves: Meliphagidae).

RESULTS

We consider the influence of range size, shape, and position (latitudinal and longitudinal midpoints, island or continental species), and consider two traits known to influence range size: dispersal ability and body size. Applying several analytical approaches, including phylogenetic Bayesian path analysis, spatiophylogenetic models, and state-dependent speciation and extinction models, we find support for both the positive relationship between range size and speciation rate and the influence of mode of speciation.

CONCLUSIONS

Honeyeater speciation rate differs considerably between islands and the continental setting across the clade's distribution, with range size contributing positively in the continental setting, while dispersal ability influences speciation regardless of setting. These outcomes support Darwin's original proposal for a positive relationship between range size and speciation likelihood, while extending the evidence for the contribution of dispersal ability to speciation.

Competition and geography underlie speciation and morphological evolution in Indo-Australasian monitor lizards

How biotic and abiotic factors act together to shape biological diversity is a major question in evolutionary biology. The recent availability of large datasets and development of new methodological approaches provide new tools to evaluate the predicted effects of ecological interactions and geography on lineage diversification and phenotypic evolution. Here, we use a near complete phylogenomic-scale phylogeny and a comprehensive morphological dataset comprising more than a thousand specimens to assess the role of biotic and abiotic processes in the diversification of monitor lizards (Varanidae). This charismatic group of lizards shows striking variation in species richness among its clades and multiple instances of endemic radiation in Indo-Australasia (i.e., the Indo-Australian Archipelago and Australia), one of Earth's most biogeographically complex regions. We found heterogeneity in diversification dynamics across the family. Idiosyncratic biotic and geographic conditions appear to have driven diversification and morphological evolution in three endemic Indo-Australasian radiations. Furthermore, incumbency effects partially explain patterns in the biotic exchange between Australia and New Guinea. Our results offer insight into the dynamic history of Indo-Australasia, the evolutionary significance of competition, and the long-term consequences of incumbency effects.

Seasonal environments drive convergent evolution of a faster pace-of-life in tropical butterflies

New ecological niches that may arise due to climate change can trigger diversification, but their colonisation often requires adaptations in a suite of life-history traits. We test this hypothesis in species-rich Mycalesina butterflies that have undergone parallel radiations in Africa, Asia, and Madagascar. First, our ancestral state reconstruction of habitat preference, using c. 85% of extant species, revealed that early forest-linked lineages began to invade seasonal savannahs during the late Miocene-Pliocene. Second, rearing replicate pairs of forest and savannah species from the African and Malagasy radiation in a common garden experiment, and utilising published data from the Asian radiation, demonstrated that savannah species consistently develop faster, have smaller bodies, higher fecundity with an earlier investment in reproduction, and reduced longevity, compared to forest species across all three radiations. We argue that time-constraints for reproduction favoured the evolution of a faster pace-of-life in savannah species that facilitated their persistence in seasonal habitats.

Macroevolutionary dynamics of parasite diversification: A reality check

Parasitism is often invoked as a factor explaining the variation in diversification rates across the tree of life, while also representing up to half of Earth's diversity. Yet, patterns and processes of parasite diversification remain mostly unknown. In this study, we assess the patterns of parasite diversification and specifically determine the role of life-history traits (i.e. life cycle complexity and host range) and major coevolutionary events in driving diversification across eight phylogenetic datasets spanning taxonomically different parasite groups. Aware of the degree of incomplete sampling among all parasite phylogenies, we also tested the impact of sampling bias on estimates of diversification. We show that the patterns and rates of parasite diversification differ among taxa according to life cycle complexity and to some extent major host transitions. Only directly transmitted parasites were found to be influenced by an effect of major host transitions on diversification rates. Although parasitism may be a main factor responsible for heterogeneity in diversification among the tree of life, the high degree of incomplete parasite phylogenies remains an obstacle when modelling diversification dynamics. Nevertheless, we provide the first comparative test of parasite diversification, revealing some consistent patterns and insight into the processes that shape it.

Increased diversification rates are coupled with higher rates of climate space exploration in Australian Acacia (Caesalpinioideae)

Australia is an excellent setting to explore relationships between climate change and diversification dynamics. Aridification since the Eocene has resulted in spectacular radiations within one or more Australian biomes. Acacia is the largest plant genus on the Australian continent, with around 1000 species, and is present in all biomes. We investigated the macroevolutionary dynamics of Acacia within climate space. We analysed phylogenetic and climatic data for 503 Acacia species to estimate a time-calibrated phylogeny and central climatic tendencies for BioClim layers from 132 000 herbarium specimens. Diversification rate heterogeneity and rates of climate space exploration were tested. We inferred two diversification rate increases, both associated with significantly higher rates of climate space exploration. Observed spikes in climate disparity within the Pleistocene correspond with onset of Pleistocene glacial-interglacial cycling. Positive time dependency in environmental disparity applies in the basal grade of Acacia, though climate space exploration rates were lower. Incongruence between rates of climate space exploration and disparity suggests different Acacia lineages have experienced different macroevolutionary processes. The second diversification rate increase is associated with a south-east Australian mesic lineage, suggesting adaptations to progressively aridifying environments and ability to transition into mesic environments contributed to Acacia's dominance across Australia.

Digest: The evolutionary relationship between environment and size in Australian rodents

Biome shifts are thought to be relatively rare, but some clades shift among starkly different environments with relative ease. What causes these shifts, and how do they shape phenotypic evolution? Roycroft et al. found that biome shifts in the Pseudomys Division of murid rodents were repeatedly accompanied by body size evolution in accordance with Bergmann's rule, suggesting adaptive evolution in response to changing climate conditions.

Digital dissection of the head of the rock dove (Columba livia) using contrast-enhanced computed tomography

The rock dove (or common pigeon), Columba livia, is an important model organism in biological studies, including research focusing on head muscle anatomy, feeding kinematics, and cranial kinesis. However, no integrated computer-based biomechanical model of the pigeon head has yet been attempted. As an initial step towards achieving this goal, we present the first three-dimensional digital dissection of the pigeon head based on a contrast-enhanced computed tomographic dataset achieved using iodine potassium iodide as a staining agent. Our datasets enable us to visualize the skeletal and muscular anatomy, brain and cranial nerves, and major sense organs of the pigeon, including very small and fragile features, as well as maintaining the three-dimensional topology of anatomical structures. This work updates and supplements earlier anatomical work on this widely used laboratory organism. We resolve several key points of disagreement arising from previous descriptions of pigeon anatomy, including the precise arrangement of the external adductor muscles and their relationship to the posterior adductor. Examination of the eye muscles highlights differences between avian taxa and shows that pigeon eye muscles are more similar to those of a tinamou than they are to those of a house sparrow. Furthermore, we present our three-dimensional data as publicly accessible files for further research and education purposes. Digital dissection permits exceptional visualisation and will be a valuable resource for further investigations into the head anatomy of other bird species, as well as efforts to reconstruct soft tissues in fossil archosaurs.