International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.4, 147-161 http://ecoevopublisher.com/index.php/ijmeb 149 3.2 Sympatric speciation Sympatric speciation occurs without geographic isolation, often driven by ecological niche differentiation or sexual selection. This mechanism is more controversial but has been supported by several case studies. In the Hydrobatinae subfamily of storm-petrels, sympatric speciation by allochrony (seasonal breeding differences) has been suggested. For instance, Hydrobates castro and H. monteiroi breed in different seasons on the Azores, indicating reproductive isolation without geographic separation (Figure 1) (Wallace et al., 2017). Figure 1 The evolutionary relationships and breeding season differences among various species of the Hydrobatinae subfamily (storm-petrels) (Adapted from Wallace et al., 2017) Image caption: The branch lengths represent genetic differences between species, with the values (such as 1.0 and 0.81) indicating node support values. The higher the support value, the higher the credibility of the branch. The upper right corner of the figure shows the significant differences in breeding seasons between H. castro and H. monteiroi in the Azores. The scale bar (0.002) at the bottom of the figure represents the branch lengths in the phylogenetic tree (Adapted from Wallace et al., 2017) 3.3 Peripatric and parapatric speciation In peripatric speciation, small peripheral populations experience strong genetic drift and selection pressures, leading to rapid divergence. Parapatric speciation involves populations that are adjacent but experience different selective pressures across an environmental gradient. Peripheral isolates: The land snail genus Theba on the Canary Islands demonstrates peripatric speciation. Cryptic diversification driven by non-adaptive allopatric differentiation and secondary gene flow has been observed, with some sympatric forms showing complete reproductive isolation (Greve et al., 2012). Hybrid zones: In the Cuban green anoles, partial island submergence during the Miocene led to allopatric speciation. Subsequent unification of Cuba allowed for secondary contact, with distinct species maintaining their identity despite occasional hybridization, indicating a role for hybrid zones in speciation (Glor et al., 2004). 4 Adaptive Radiation in Vertebrates 4.1 Concept and significance of adaptive radiation Adaptive radiation is a fundamental concept in evolutionary biology, referring to the rapid diversification of a single ancestral species into multiple species, each adapted to exploit different ecological niches. This process is significant because it explains how a single lineage can give rise to a wide variety of forms and functions, contributing to the biodiversity we observe today. Conditions that favor adaptive radiation include the availability of unoccupied niches, ecological opportunities, and key innovations that allow organisms to exploit new resources or environments (Pincheira-Donoso et al., 2015). The 2018 American Genetic Association meeting held in
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