Data from: Experimental manipulation of polyandry in a marine gastropod reveals how the number of mates affects reproductive output, offspring size, and the distribution of paternity within broods

Polyandry, where females mate with multiple males, often mediates how
ecological and evolutionary forces shape populations, with various
explanations for why it occurs. However, these explanations often stem
from separate studies on model species, field observations, or lab
experiments. Given polyandry's potential context-dependent effects,
it is crucial to design studies that concurrently test multiple hypotheses
within wild populations. Therefore, we conducted two experiments over two
years that experimentally manipulated the number of males a female mates
with in the marine gastropod, the Florida crown conch (Melongena corona).
We tested whether experimentally increasing polyandry leads to more
offspring, larger offspring at hatching, and broods with greater variation
in offspring size and higher genetic diversity. We also investigated
paternity skew, the effects of mate order, male size, and copulating time
on paternity. We genotyped 3,157 offspring from 20 mothers to quantify
paternity share at hatching. We found that females mating with more males
did not produce more offspring or larger offspring than monandrous females
at the embryo or hatching stage. However, multiple mating increased
within-brood variation in offspring size at hatching, possibly as a
response to exploitative intracapsular competition for oxygen in mixed
broods or sire effects. Paternity share within broods at hatching was
skewed, rather than evenly distributed, resulting in a lower effective
number of sires compared to the number of mates. Paternity share per brood
declined with mate order and increased with copulation duration, but was
unaffected by male size. Overall, the commonly hypothesized consequences
of polyandry were not observed in our experiments. Instead, we hypothesize
that multiple mating in this species arises from convenience polyandry or
mate encounter rates.