Abstract
Theory shows that polyandry (mating with multiple males within a reproductive season) works as bet-hedging to increase the geometric mean fitness (GMF) of polyandrous genotype over generations and avoid extinction but it was rarely tested empirically. In this study, we distributed the eggs of Gryllus bimaculatus females mated with 1–4 males (mating treatment) into 4 petri dishes with different conditions: 25 °C/fresh water, 37 °C/fresh water, 25 °C/salt water, 37 °C/salt water, simulating 4 clutches laid at the different sites are suffered environmental change. The egg hatching rate was obtained over 7 blocks with different females for each mating treatment. In general, significantly more eggs hatched in 25 °C than 37 °C and in fresh water than salt water. The reproductive failure (no hatched eggs per petri dish) frequently occurred in monandry and 2-male polyandry. Next, we considered 7 blocks as the successive 7 virtual generations and calculated the within-generation arithmetic mean fitness (AMF) among females of the same treatment and the between-generation GMF of the AMF across 7 generations. Randomization test shows that the GMF of 3- and 4-male polyandry were significantly higher than monandry. This study shows that the risk from mating only once can be avoided by polyandrous mating as bet-hedging.
Highlights
Male fitness is positively correlated with the number of mates that he acquires, and the adaptive significance of male multiple mating is understandable (Thornhill and Alcock 1983; Shuker and Simmons 2014; Simmons 2019)
Out of 200 eggs each collected from female 6–2 (2P), 6–3 (2P), 7–3 (2P) and 7–4 (3P), 100 eggs allocated to the salinity conditions were dead before the swelling but remaining 100 eggs allocated to the fresh water condition were developed further
This study shows that 3 different types of bet-hedging worked in the crickets as follows: (1) the bet-hedging polyandry to avoid male-caused reproductive failures, (2) metapopulation bet-hedging to spread the extinction risks over multiple habitats and (3) reproduction itself as bet-hedging
Summary
Male fitness is positively correlated with the number of mates that he acquires, and the adaptive significance of male multiple mating (polygyny) is understandable (Thornhill and Alcock 1983; Shuker and Simmons 2014; Simmons 2019). The causes and consequences of polyandry have stimulated many researchers as an unsolved enigma in evolutionary biology (Walker 1980; Thornhill and Alcock 1983; Birkhead and Møller 1992; Yasui 1997, 1998, 2001; Arnqvist and Nilsson 2000; Simmons 2005; Jennions and Petrie 2007; Garcia-Gonzalez et al 2015; Yasui and GarciaGonzalez 2016; Yasui and Yoshimura 2018). Direct or environmental benefits (e.g., replenishment of sperm supply, nutritional nuptial gift, paternal care of offspring and protection against predators or sexual harassment from other males; Arnqvist and Nilsson 2000) are convincing because the cost for females are paid within generation (Yasui 1998). Despite several theoretical models (Curtsinger 1991; Yasui 1997, 1998, 2001; Yasui and Garcia-Gonzalez 2016; Yasui and Yoshimura 2018) showed
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