Data from: The more the better – polyandry and genetic similarity are positively linked to reproductive success in a natural population of terrestrial salamanders (Salamandra salamandra)

Although classically thought to be rare, female polyandry is wide-spread
and may entail significant fitness benefits. If females store sperm over
extended periods of time, the consequences of polyandry will depend on the
pattern of sperm storage, and some of the potential benefits of polyandry
can only be realized if sperm from different males is mixed. Our study
aimed to determine patterns and consequences of polyandry in an amphibian
species, the fire salamander, under fully natural conditions. Fire
salamanders are ideal study objects, since mating, fertilisation and
larval deposition are temporally decoupled, females store sperm for
several months and larvae are deposited in the order of fertilization.
Based on 18 microsatellite loci, we conducted paternity analysis of 24
female-offspring arrays, with, in total, over 600 larvae fertilised under
complete natural conditions. More than one third of females were
polyandrous and up to four males were found as sires. Our data clearly
show that sperm from multiple males is mixed in the female's
spermatheca. Nevertheless, paternity is biased, and the most successful
male sires on average 70% of the larvae, suggesting a “topping off”
mechanism with first-male precedence. Female reproductive success
increased with the number of sires, most likely because multiple mating
ensured high fertilization success. In contrast, offspring number was
unaffected by female condition and genetic characteristics, but
surprisingly, it increased with the degree of genetic relatedness between
females and their sires. Sires of polyandrous females tended to be
genetically similar to each other, indicating a role for active female
choice.