Integrated Population Genomic Analysis and Numerical Simulation to Estimate Larval Dispersal of Acanthaster cf. solaris Between Ogasawara and Other Japanese Regions

The estimation of larval dispersal on an ecological timescale is significant for conservation of marine species. In 2018, a semi-population outbreak of crown-of-thorns sea star, Acanthaster cf. solaris, was observed on a relatively isolated oceanic island, Ogasawara. The aim of this study was to assess whether this population outbreak was caused by large-scale larval recruitment (termed secondary outbreak) from the Kuroshio region. We estimated larval dispersal of the coral predator A. cf. solaris between the Kuroshio and Ogasawara regions using both population genomic analysis and simulation of oceanographic dispersal. Population genomic analysis revealed overall genetically homogenized patterns among Ogasawara and other Japanese populations, suggesting that the origin of the populations in the two regions is the same. In contrast, a simulation of 26-year oceanographic dispersal indicated that larvae are mostly self-seeded in Ogasawara populations and have difficulty reaching Ogasawara from the Kuroshio region within one generation. However, a connectivity matrix produced by the larval dispersal simulation assuming a Markov chain indicated gradual larval dispersal migration from the Kuroshio region to Ogasawara in a stepping-stone manner over multiple years. These results suggest that the 2018 outbreak was likely the result of self-seeding, including possible inbreeding (as evidenced by clonemate analysis), as large-scale larval dispersal from the Kurishio population to the Ogasawara population within one generation is unlikely. Instead, the population in Ogasawara is basically sustained by self-seedings, and the outbreak in 2018 was also most likely caused by successful self-seedings including possible inbreeding, as evidenced by clonemate analysis. This study also highlighted the importance of using both genomic and oceanographic methods to estimate larval dispersal, which provides significant insight into larval dispersal that occurs on ecological and evolutionary timescales.

Population genomic structure in Goodman's mouse lemur reveals long-standing separation of Madagascar's Central Highlands and eastern rainforests

Madagascar’s Central Highlands are largely composed of grasslands, interspersed with patches of forest. The pre-human extent of these grasslands is a topic of vigorous debate, with conventional wisdom holding that they are anthropogenic in nature and emerging evidence supporting that grasslands were a component of the pre-human Central Highlands vegetation. Here, we shed light on the temporal dynamics of Madagascar’s vegetative composition by conducting a population genomic investigation of Goodman’s mouse lemur (Microcebus lehilahytsara; Cheirogaleidae). These small-bodied primates occur both in Madagascar’s eastern rainforests and in the Central Highlands, which makes them a valuable indicator species. Population divergences among forest-dwelling mammals can serve as a proxy for habitat fragmentation and patterns of post-divergence gene flow can reveal potential migration corridors consistent with a wooded grassland mosiac. We used RADseq data to infer phylogenetic relationships, population structure, demographic models of post-divergence gene flow, and population size change through time. These analyses offer evidence that open habitats are an ancient component of the Central Highlands, and that wide-spread forest fragmentation occurred naturally during a period of decreased precipitation near the last glacial maximum. Models of gene flow suggest that migration across the Central Highlands has been possible from the Pleistocene through the recent Holocene via riparian corridors. Notably, though our findings support the hypothesis that Central Highland grasslands predate human arrival, we also find evidence for human-mediated population declines. This highlights the extent to which species imminently threatened by human-mediated deforestation may be more vulnerable from paleoclimatic changes.

The recombination landscapes of spiny lizards (genus Sceloporus)

Despite playing a critical role in evolutionary processes and outcomes, relatively little is known about rates of recombination in the vast majority of species, including squamate reptiles—the second largest order of extant vertebrates, many species of which serve as important model organisms in evolutionary and ecological studies. This paucity of data has resulted in limited resolution on questions related to the causes and consequences of rate variation between species and populations, the determinants of within-genome rate variation, as well as the general tempo of recombination rate evolution on this branch of the tree of life. In order to address these questions, it is thus necessary to begin broadening our phylogenetic sampling. We here provide the first fine-scale recombination maps for two species of spiny lizards, Sceloporus jarrovii and Sceloporus megalepidurus, which diverged at least 12 Mya. As might be expected from similarities in karyotype, population-scaled recombination landscapes are largely conserved on the broad-scale. At the same time, considerable variation exists at the fine-scale, highlighting the importance of incorporating species-specific recombination maps in future population genomic studies.