Bracketing phenogenotypic limits of mammalian hybridization

Abstract

An increasing number of mammalian species have been shown to have a history of hybridization and introgression based on genetic analyses. Only relatively few fossils, however, preserve genetic material, and morphology must be used to identify the species and determine whether morphologically intermediate fossils could represent hybrids. Because dental and cranial fossils are typically the key body parts studied in mammalian palaeontology, here we bracket the potential for phenotypically extreme hybridizations by examining uniquely preserved cranio-dental material of a captive hybrid between grey and ringed seals. We analysed how distinct these species are genetically and morphologically, how easy it is to identify the hybrids using morphology and whether comparable hybridizations happen in the wild. We show that the genetic distance between these species is more than twice the modern human–Neanderthal distance, but still within that of morphologically similar species pairs known to hybridize. By contrast, morphological and developmental analyses show grey and ringed seals to be highly disparate, and that the hybrid is a predictable intermediate. Genetic analyses of the parent populations reveal introgression in the wild, suggesting that grey–ringed seal hybridization is not limited to captivity. Taken together, we postulate that there is considerable potential for mammalian hybridization between phenotypically disparate taxa.

Male grey seal commits fatal sexual interaction with adult female harbour seals in the German Wadden Sea

“…Injuries during interspecific interactions become more likely if there is great disparity in size and weight 52 . This is also reported for the here involved species, as a juvenile or young adult grey seal bull can easily over-power and subdue a female harbour seal 25,26,60 . The behavioural response of the female during mating is important for the stimulation of the male.…”

Identifying early stages of reindeer domestication in the archaeological record: a 3D morphological investigation on forelimb bones of modern populations from Fennoscandia

“…Although we have not been able to include hybrid individuals in our study, the main problem of their presence in archaeological contexts could be the potential large overlap between hybrids and their parents in terms of morphometric diversity. Indeed, hybrids can present morphological traits more similar to a particular parent, as well as an intermediate morphology and size (Evin et al 2015 ; Hanot et al 2017 , 2019 ; Hanot and Bochaton 2018 ; Savriama et al 2018 ).…”

Unravelling the hybrid vigor in domestic equids: the effect of hybridization on bone shape variation and covariation

“…The fact that mules and hinnies are (with only a few exceptions) sterile [19, 20] probably contributes to the low attention paid to the morphological consequences of hybridization in domestic equids. Indeed, evolutionary studies usually focus on this process in a context of speciation or introgression [21–24]. Moreover, no macroscopic feature specific to hybrid bones has been, for now, identified (in a context in which horse and donkey bones are themselves hard to distinguish) [25], which would suggest the absence of strongly transgressive morphologies related to hybridization in domestic equids.…”

“…This is especially interesting in the study of hybridization knowing that hybridization has been suspected to sometimes disrupt developmental regulation [46, 47]. This issue is moreover particularly relevant in the case of the horse and the donkey, known to show (in comparison with other hybridizing mammals) a high genetic distance [24].…”