Does polyandry really pay off? The effects of multiple mating and number of fathers on morphological traits and survival in clutches of nesting green turtles at Tortuguero.

Alonzo Alfaro-Núñez,Michael P. Jensen,F. Alberto Abreu-Grobois

doi:10.7717/peerj.880

Abstract

Despite the long debate of whether or not multiple mating benefits the offspring, studies still show contradictory results. Multiple mating takes time and energy. Thus, if females fertilize their eggs with a single mating, why to mate more than once? We investigated and inferred paternal identity and number of sires in 12 clutches (240 hatchlings) of green turtles (Chelonia mydas) nests at Tortuguero, Costa Rica. Paternal alleles were inferred through comparison of maternal and hatchling genotypes, and indicated multiple paternity in at least 11 of the clutches (92%). The inferred average number of fathers was three (ranging from 1 to 5). Moreover, regression analyses were used to investigate for correlation of inferred clutch paternity with morphological traits of hatchlings fitness (emergence success, length, weight and crawling speed), the size of the mother, and an environmental variable (incubation temperature). We suggest and propose two different comparative approaches for evaluating morphological traits and clutch paternity, in order to infer greater offspring survival. First, clutches coded by the exact number of fathers and second by the exact paternal contribution (fathers who gives greater proportion of the offspring per nest). We found significant differences (P < 0.05) in clutches coded by the exact number of fathers for all morphological traits. A general tendency of higher values in offspring sired by two to three fathers was observed for the length and weight traits. However, emergence success and crawling speed showed different trends which unable us to reach any further conclusion. The second approach analysing the paternal contribution showed no significant difference (P > 0.05) for any of the traits. We conclude that multiple paternity does not provide any extra benefit in the morphological fitness traits or the survival of the offspring, when analysed following the proposed comparative statistical methods.

Highlights

The fertilization of eggs in many female animals is usually achieved through a single mating, multiple mating is a relatively common observation in natural populations
Multiple mating The observation of a multiple paternity (MP) frequency of at least 92% in this study is the highest ever recorded for green turtles
MP was previously reported for green turtles at Tortuguero with a frequency of 50% (Bjorndal, Bolten & Troeng)

Summary

Introduction

The fertilization of eggs in many female animals is usually achieved through a single mating, multiple mating is a relatively common observation in natural populations. Sperm from different males may compete to fertilize a single clutch of eggs. This is the case in many species of insects, gastropods, fish, amphibian, birds and reptiles (FitzSimmons, 1998; Garcia-Vazquez, 2001; Jones & Clark, 2003; Garcıa-Gonzalez & Simmons, 2005; Chandler & Zamudio, 2008; Beese et al, 2008; Noble, Keogh & Whiting, 2013; LaBrecque et al, 2014) or in progeny from the same brood in mammals (Clapham & Palsbøll, 1997; Shurtliff, Pearse & Rogers, 2005). Sperm competition may be an important factor in the evolution of reproduction of many organisms, the precise mechanism that determines sperm success is not fully understood (Jones & Clark, 2003)

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