Abstract
Hybridization and introgression are evolutionarily significant phenomena breaking down species boundaries. “Hybrid zones” (regions of species overlap and hybridization) enable quantification of hybridization frequency and examination of mechanisms driving and maintaining gene flow. The hybrid anemonefish Amphiprion leucokranos is found where parent species (A. chrysopterus; A. sandaracinos) distributions overlap. Here, we examine geographic variation in hybridization and introgression, and potential impacts on parent species integrity through assessing relative abundance, social group composition, and genetic structure (mtDNA cytochrome b, 21 microsatellite loci) of taxa at three hybrid zone locations: Kimbe Bay (KB) and Kavieng (KA), Papua New Guinea; the Solomon Islands (SO). Relative abundances of and size disparities between parent species apparently drive hybridization frequency, introgression patterns, and genetic composition of taxa. Conspecific groups are most common in KB (65%) where parent species are similarly abundant. Conversely, mixed species groups dominate SO (82%), where A. chrysopterus is more abundant. Hybrids most commonly cohabit with A. sandaracinos in KB (17%), but with A. chrysopterus in KA (22%) and SO (50%). Genetic differentiation (nDNA) analyses indicate that parent species remain distinct, despite ongoing hybridization and hybrids are genetically similar to A. sandaracinos—resulting from persistent backcrossing with this smallest species. This study shows that hybridization outcomes may depend on the social and ecological context in which taxa hybridize, where relative abundance and disparate size of parent species explain the frequency and patterns of hybridization and introgression in the A. leucokranos hybrid zone, reflecting size‐based dominance behaviors of anemonefish social groups.
Highlights
Hybridization among closely related species is common and can play a significant role in evolution and speciation (Mallet, 2005)
Departure from Hardy–Weinberg equilibrium (HWE) at locus As20, with homozygous excess revealed during analysis may be influenced by a null allele
Genotypic diversity, based on microsatellite data, was moderate to high (0.478 ± 0.25 to 0.742 ± 0.37), with greater genotypic diversity estimates for hybrid populations compared with parent taxa across all three regions (Table 1)
Summary
Hybridization among closely related species is common and can play a significant role in evolution and speciation (Mallet, 2005). The outcomes of hybridization events are diverse, include fusion of species, reinforcement of reproductive barriers, and generation of new distinct populations of mixed ancestry, and may provide the foundation for speciation and diversification to occur (Abbott, Hegarty, Hiscock, & Brennan, 2010; Mallet, 2007,; Meier et al, 2017; Servedio & Noor, 2003; Taylor et al, 2006; Via, 2009; Wu, 2001). Studying young hybrid taxa allows contemporary insights into potential speciation events or species coalescence in progress, occurring at secondary contact zones between closely related taxa that may be undergoing rapid adaptive radiations (Gourbiere & Mallet, 2010; Meier et al, 2017; Price & Bouvier, 2002; Seehausen, 2004). In nature the mechanisms driving and maintaining hybridization, determining patterns of introgression, and maintaining species integrity remain poorly understood
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
