Abstract
Most genetic surveys of parentage in nature sample only a small fraction of the breeding population. Here we apply microsatellite markers to deduce the genetic mating system and assess the reproductive success of females and males in an extensively collected, semi-closed stream population of the mottled sculpin fish, Cottus bairdi. In this species, males guard nest rocks where females deposit the eggs for fertilization. The potential exists for both males and females to mate with multiple partners and for males to provide parental care to genetically unrelated offspring. Four hundred and fifty-five adults and subadults, as well as 1,259 offspring from 23 nests, were genotyped at five polymorphic microsatellite loci. Multilocus maternal genotypes, deduced via genetic analyses of embryos, were reconstructed for more than 90% of the analysed nests, thus allowing both male and female reproductive success to be estimated accurately. There was no genetic evidence for cuckoldry, but one nest probably represents a takeover event. Successful males spawned with a mean of 2.8 partners, whereas each female apparently deposited her entire clutch of eggs in a single nest (mean fecundity = 66 eggs/female). On average, genetically deduced sires and dams were captured 1.6 and 9.3 metres from their respective nests, indicating little movement by breeders during the spawning season. Based on a 'genetic mark-recapture' estimate, the total number of potentially breeding adults (c. 570) was an order-of-magnitude larger than genetically based estimates of the effective number of breeders (c. 54). In addition, significantly fewer eggs per female were deposited in single than in multidam nests. Not only were perceived high-quality males spawning with multiple partners, but they were receiving more eggs from each female.
Highlights
Genetic analyses of fish reproduction in nature have provided insights into broader aspects of animal mating system evolution
The population was semi-closed: the downstream point was marked by a pipeline crossing the creek, and the upstream end was blocked by a weir about 50 m beyond the study area
Previous behavioural research has addressed the reproductive biology of the mottled sculpin, Cottus bairdi
Summary
Genetic analyses of fish reproduction in nature have provided insights into broader aspects of animal mating system evolution (reviewed in Avise 2001; Avise et al 2002). In the current study of the mottled sculpin (Cottus bairdi) we have characterized matings and reproductive success for nearly an entire local deme within a typical southern Appalachian stream. Mottled sculpins are good subjects for genetic analyses as they generally have restrictive movement patterns (Downhower & Brown 1979, 1980; Hill & Grossman 1987; Petty 1998) and their highly conspicuous nests are frequently found at moderate to high densities These features allowed us to collect and examine a large fraction of nests and putative parents (of both sexes) from a section of stream housing a fairly closed breeding population
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