title: Intermittent breeding and constraints on litter size: consequences for effective population size per generation (Ne ) and per reproductive cycle (Nb ).
abstract: In iteroparous species, it is easier to estimate Nb (effective number of breeders in one reproductive cycle) than Ne (effective population size per generation). Nb can be used as a proxy for Ne and also can provide crucial insights into eco-evolutionary processes that occur during reproduction. We used analytical and numerical methods to evaluate effects of intermittent breeding and litter/clutch size on inbreeding Nb and Ne . Fixed or random litter sizes ≥ 3 have little effect on either effective-size parameter; however, in species (e.g., many large mammals) in which females can produce only one offspring per cycle, female Nb  = ∞ and overall Nb  = 4Nb (male) . Intermittent breeding reduces the pool of female breeders, which reduces both female and overall Nb ; reductions are larger in high-fecundity species with high juvenile mortality and increase when multiple reproductive cycles are skipped. Simulated data for six model species showed that both intermittent breeding and litter-size constraints increase Ne , but only slightly. We show how to quantitatively account for these effects, which are important to consider when (1) using Nb to estimate Ne , or (2) drawing inferences about male reproductive success based on estimates of female Nb .
authors.affiliation: Northwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, Seattle, Washington, 98112. robin.waples@noaa.gov.
authors.forename: Robin S
authors.initials: RS
authors.lastname: Waples
authors.forename: Tiago
authors.initials: T
authors.lastname: Antao
mesh_terms: D000818:Animals; D001947:Breeding; D052284:Clutch Size / Q000235:genetics; D005260:Female; D005298:Fertility / Q000235:genetics; D008098:Litter Size / Q000235:genetics*; D008297:Male; D008957:Models, Genetic; D011153:Population / Q000235:genetics; D012098:Reproduction / Q000235:genetics
keywords: Clutch size; computer simulations; intermittent breeding; iteroparity; overlapping generations