Abstract
Multiple paternity appears to be a common trait of elasmobranch mating systems, with its occurrence likely driven by convenience, due to females seeking to minimize the stress of male harassment. Here we use molecular markers to analyse the frequency of multiple paternity in two related viviparous sharks, Mustelus mustelus and Mustelus punctulatus. We first applied molecular methods to assign pregnant females, embryos and additional reference adults (N = 792) to one of the two species. Paternity analysis was performed using a total of 9 polymorphic microsatellites on 19 females and 204 embryos of M. mustelus, and on 13 females and 303 embryos of M. punctulatus. Multiple paternity occurs in both species, with 47% of M. mustelus and 54% of M. punctulatus litters sired by at least two fathers. Female fecundity is not influenced by multiple mating and in 56% of polyandrous litters paternity is skewed, with one male siring most of the pups. Genetic analyses also revealed hybridization between the two species, with a M. punctulatus female bearing pups sired by a M. mustelus male. The frequency of polyandrous litters in these species is consistent with aspects of their reproductive biology, such as synchronous ovulation and possible occurrence of breeding aggregations.
Highlights
Frequency of genetic polyandry in elasmobranchs does not necessarily reflect the level of polyandrous mating behaviour[7,11], since paternity may be highly influenced by post-copulatory and/or post-zygotic mechanisms[7,25]
We detected multiple paternity in both Mustelus mustelus and M. punctulatus, confirming our expectations based on the ubiquitous presence of polyandrous litters in elasmobranch species[7,9,10,11,12]
Around half of the litters are sired by multiple males, a frequency intermediate to those reported in other elasmobranchs where the great majority of the litters are either monandrous[17,18] or polyandrous[13,15,16,20]
Summary
Frequency of genetic polyandry in elasmobranchs does not necessarily reflect the level of polyandrous mating behaviour[7,11], since paternity may be highly influenced by post-copulatory and/or post-zygotic mechanisms[7,25]. Two out of 507 embryos, collected from one single M. punctulatus female (Mp1_6.9) sampled in the northern Adriatic Sea, besides being classified as M. punctulatus using the mtDNA COI test, showed a mixed genotype at the 6 microsatellite loci used for identification[39] (Table 1 and Supplementary Data S1).
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