The loss of sperm storage ability in females as a potential driver for increase extinction in Chondrichthyes

Abstract

Sperm storage in females (SS) has been reported in Chondrichthyans species, and involves the prolonged maintenance of viable sperm after mating events, prior to egg fertilization. Along with multiple paternity (MP – female producing Offspring of multiple males within the same litter), SS has been hypothesized to be related to the increased reproductive fitness of cartilaginous fish lineages. The present study aims to investigate if: (1) are SS and MP evolutionarily related and share the same evolutionary history in Chondrichthyes? (2) How the presence of SS is implied in the extinction and speciation rates and thus related to the current species diversity of the group? To answer these questions, we obtained SS and MP records for Chondrichthyes species from the literature and performed ancestral reconstruction analyses for each character in the phylogenetic. We employed MEDUSA and MiSSE to detect if shifts in diversification rates were related to characters along the phylogeny. Finally, we utilized HiSSE to calculate the net diversity rates for observed and unobserved states. The ancestral reconstruction indicates that both characters are plesiomorphic for the group, SS is suggested to be absent in Lamniformes and Rhinopristiformes, whereas MP may be absent in Galeocerdo cuvier. MEDUSA and MiSSE detected that all clades lacking SS showed no increase in rates, whileareas higher diversification rates in clades with SS. HiSSE identified lower net diversity rates in clades with lacking SS associated with hidden states. Therefore, SS seem to contribute to increase extinction rates by reducing diversity among the Chondricthyes.