Hybridization in the Cetacea: widespread occurrence and associated morphological, behavioral, and ecological factors

Abstract

Hybridization has been documented in a many different pairs of cetacean species both in captivity and in the wild. The widespread occurrence of hybridization indicates that postmating barriers to interbreeding are incomplete within the order Cetacea, and therefore raises questions about how species integrity is maintained in the face of interspecific (and often intergeneric) gene flow. We examined hybridization across the order Cetacea (oceanic species included: N = 78; species with 44 chromosomes included: N = 52) to test for associations between the occurrence of hybridization and similarity across 13 ecological, morphological and behavioral traits in hybridizing vs. non‐hybridizing species pairs. We found that species pairs that share a greater number of traits had a higher propensity to hybridize than pairs of species that did not. This trend was driven by behavioral and morphological traits such as vocalization frequency and body size. Together our findings suggest the importance of divergent selection on morphological and behavioral traits within sympatric species in constraining opportunities for hybridization and preventing the collapse of parental species.

Asymmetric and Spiraled Genitalia Coevolve with Unique Lateralized Mating Behavior

“…The close genital correspondence could be the result of several potential coevolutionary mechanisms, including sexual conflict, female choice, and "lock-and-key". As hybridization is common among cetaceans 41 , it is unlikely a "lock-and-key" mechanism, and the close correspondence likely arises as a result of an intersexual evolutionary arms race in harbor porpoises. In the San Francisco Bay population, males initiate all mating events, attempt copulations throughout the year, do not engage in pre-copulatory courtship, and approach females in all reproductive states 7 .…”

A Robust Design Capture-Recapture Analysis of Abundance, Survival and Temporary Emigration of Three Odontocete Species in the Gulf of Corinth, Greece

“…An additional threat in the Gulf of Corinth may be hybridization with striped dolphins. Hybridization among Delphininae is not rare, with many intergeneric and intrageneric pairs of species able to produce viable hybrid offsprings, and in at least some cases viable backcrosses [85]. Hybridization is a relatively unexplored cause of extinction, especially for small populations that mix with more abundant ones [86, 87].…”

Post-glacial habitat release and incipient speciation in the genus Delphinus

“…Two putative hybrids were detected and both IMa and BayesAss suggested biased gene flow from the sbENP to the lbENP form at nonzero levels. This is not necessarily inconsistent with incipient speciation, as hybrids between recognized species are common for cetaceans (see Crossman et al, 2016), and incipient speciation is possible even in the face of recurrent or continuous gene flow (Hey, 2006;Niemiller et al, 2008), for example, among three divergent forms of Tennessee cave salamander, Gyrinophilus palleucus (Niemiller et al, 2008). Incomplete lineage sorting could explain some missassigned individuals based on a given marker, but the congruence of phenotype and different marker types for the same individuals makes this interpretation less likely.…”