Genetic and Ecogeographic Controls on Species Cohesion in Australia's Most Diverse Lizard Radiation.

AbstractSpecies vary extensively in geographic range size and climatic niche breadth. If range limits are primarily determined by climatic factors, species with broad climatic tolerances and those that track geographically widespread climates should have large ranges. However, large ranges might increase the probability of population fragmentation and adaptive divergence, potentially decoupling climatic niche breadth and range size. Conversely, ecological generalism in large-ranged species might lead to higher gene flow across climatic transitions, increasing species' cohesion and thus decreasing genetic isolation by distance (IBD). Focusing on Australia's iconic Ctenotus lizard radiation, we ask whether species range size scales with climatic niche breadth and the degree of population isolation. To this end, we infer independently evolving operational taxonomic units (OTUs), their geographic and climatic ranges, and the strength of IBD within OTUs based on genome-wide loci from 722 individuals spanning 75 taxa. Large-ranged OTUs were common and had broader climatic niches than small-ranged OTUs; thus, large ranges do not appear to simply result from passive tracking of widespread climatic zones. OTUs with larger ranges and broader climatic niches showed relatively weaker IBD, suggesting that large-ranged species might possess intrinsic attributes that facilitate genetic cohesion across large distances and varied climates. By influencing population divergence and persistence, traits that affect species cohesion may play a central role in large-scale patterns of diversification and species richness.

Molecular phylogenetic inference of the howler monkey radiation (Primates: Alouatta).

Howler monkeys (Alouatta), comprising between nine and 14 species and ranging from southern Mexico to northern Argentina, are the most widely distributed platyrrhines. Previous phylogenetic studies of howlers have used chromosomal and morphological characters and a limited number of molecular markers; however, branching patterns conflict between studies or remain unresolved. We performed a new phylogenetic analysis of Alouatta using both concatenated and coalescent-based species tree approaches based on 14 unlinked non-coding intergenic nuclear regions. Our taxon sampling included five of the seven South American species (Alouatta caraya, Alouatta belzebul, Alouatta guariba, Alouatta seniculus, Alouatta sara) and the two recognized species from Mesoamerica (Alouatta pigra, Alouatta palliata). Similarly to previous studies, our phylogenies supported a Mesoamerican clade and a South American clade. For the South American howlers, both methods recovered the Atlantic Forest endemic A. guariba as sister to all remaining South American species, albeit with moderate support. Moreover, we found no support for the previously proposed sister relationship between A. guariba and A. belzebul. For the first time, a clade composed of A. sara and A. caraya was identified. The relationships among the other South American howlers, however, were not fully supported. Our estimates for divergence times within Alouatta are generally older compared to estimates in earlier studies. However, they conform to recent studies proposing a Miocene age for the Isthmus of Panama and for the uplift of the northern Andes. Our results also point to an early genetic isolation of A. guariba in the Atlantic Forest, in agreement with the hypothesis of biotic exchange across South American rain forests in the Miocene. Collectively, these findings contribute to a better understanding of the diversification processes among howler monkey species; however, they also suggest that further comprehension of the evolutionary history of the Alouatta radiation will rely on broadened taxonomic, geographic, and genomic sampling.