Abstract
Multiple paternity is a common phenomenon within the live-bearing fish family Poeciliidae. There is a great variety in brood sizes of at least two orders-of-magnitude across the family. However, little is known about the ramifications of this remarkable variation for the incidence and degree of multiple paternity and reproductive skew. Mollies (subgenus Mollienesia, genus Poecilia) produce some of the largest broods in the family Poeciliidae, making them an excellent model to study the effects of intra-specific variation in brood size on patterns of multiple paternity. We collected samples of the live-bearing fish Poecilia gillii from 9 locations in Costa Rica. We measured body size of 159 adult females, of which 72 were pregnant. These samples had a mean brood size of 47.2 ± 3.0 embryos, ranging from 4 to 130 embryos. We genotyped 196 field-collected specimens with 5 microsatellite markers to obtain location-specific allele frequencies. In addition, we randomly selected 31 pregnant females, genotyped all their embryos (N = 1346) and calculated two different parameters of multiple paternity: i.e., the minimum number of sires per litter using an exclusion-based method (GERUD) and the estimated number of sires per litter using a maximum likelihood approach (COLONY). Based on these two approaches, multiple paternity was detected in 22 and 27 (out of the 31) females, respectively, with the minimum number of sires ranging from 1 to 4 (mean ± SE: 2.1 ± 0.16 sires per female) and the estimated number of fathers ranging from 1 to 9 (mean ± SE: 4.2 ± 0.35 sires per female). The number of fathers per brood was positively correlated with brood size, but not with female size. Next, we calculated the reproductive skew per brood using the estimated number of sires, and found that in 21 out of the 27 multiply sired broods sires did not contribute equally to the offspring. Skew was not correlated with either female size, brood size or the number of sires per brood. Finally, we discuss several biological mechanisms that may influence multiple paternity and reproductive skew in P. gillii as well as in the Poeciliidae in general.
Highlights
Female multiple mating, or polyandry, often leads to offspring being sired by multiple fathers, a phenomenon which is referred to as multiple paternity
We show the number of alleles (NA), the allelic range, the observed (HO) and expected heterozygosity (HE), and the exclusion probability (E1) per locus and for the 5 loci combined. *This location was excluded from the multiple paternity analyses, due to the low exclusion probability
We assessed the influence of brood size and female length on the degree of multiple paternity and paternity skew in the live-bearing fish Poecilia gillii
Summary
Polyandry, often leads to offspring being sired by multiple fathers, a phenomenon which is referred to as multiple paternity. Polyandry can arise because of indirect genetic benefits (Yasui, 1998; Jennions and Petrie, 2000), in three ways: (i) Females can mate with multiple males to improve the genetic quality of the offspring by ‘trading-up’ (Pitcher et al, 2003). This hypothesis predicts that a female that mates with a ‘genetically inferior’ male can increase her fitness by mating with another male of higher genetic quality (Jennions and Petrie, 2000; Simmons, 2001; Pitcher et al, 2003), (ii) Multiple paternity can increase a female’s fitness by increasing the genetic diversity of offspring (Yasui, 1998; Fox and Rauter, 2003). Multiple paternity can arise without increasing the fitness of a female
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