Alternative Life-history Tactics Research Articles

Alternative life-history strategy contributions to effective population size in a naturally spawning salmon population.

Alternative life-history tactics are predicted to affect within-population genetic processes but have received little attention. For example, the impact of precocious males on effective population size (N e) has not been quantified directly in Pacific salmon Oncorhynchus spp., even though they can make up a large percentage of the total male spawners. We investigated the contribution of precocial males ("jacks") to N e in a naturally spawning population of Coho Salmon O. kisutch from the Auke Creek watershed in Juneau, Alaska. Mature adults that returned from 2009 to 2019 (~8000 individuals) were genotyped at 259 single-nucleotide polymorphism (SNP) loci for parentage analysis. We used demographic and genetic methods to estimate the effective number of breeders per year (N b). Jack contribution to N b was assessed by comparing values of N b calculated with and without jacks and their offspring. Over a range of N b values (108-406), the average jack contribution to N b from 2009 to 2015 was 12.9% (SE = 3.8%). Jacks consistently made up over 20% of the total male spawners. The presence of jacks did not seem to influence N b/N. The linkage disequilibrium N e estimate was lower than the demographic estimate, possibly due to immigration effects on population genetic processes: based on external marks and parentage data, we estimated that immigrant spawners produced 4.5% of all returning offspring. Our results demonstrate that jacks can influence N b and N e and can make a substantial contribution to population dynamics and conservation of threatened stocks.

Every-other-day clutch-initiation synchrony as an adaptive response to egg cannibalism in Glaucous-winged Gulls (Larus glaucescens)

Sea surface temperatures (SST) in the Pacific Northwest of North America rose 1 °C during the last half of the twentieth century. Cannibalism, a behavior observed in diverse taxa, is often associated with low food supplies, which for marine animals can be precipitated by high SSTs. In an 8 year study, we found that in years of higher sea surface temperatures, Glaucous-winged Gulls (Larus glaucescens) breeding in a colony in Washington State, Salish Sea, USA, tended to exhibit higher rates of egg cannibalism by males, higher levels of every-other-day clutch-initiation synchrony by females, and longer egg-laying seasons than in years of lower SST. Clutch-initiation synchrony increased the odds that an egg survived cannibalism and may serve as an adaptive response to egg cannibalism. Short-term climate and resource fluctuations associated with El Niño Southern Oscillation (ENSO) events may select for behavioral plasticity in marine organisms, allowing long-lived individuals such as marine birds to switch between alternative life history tactics. The implications for long-term SST warming, however, remain unknown.

Partial Migration of Fishes as Exemplified by the Estuarine‐Dependent White Perch

AbstractPartial migration defines the phenomenon of coexisting groups exhibiting migratory and resident behavior within the same population. In avian ecology, partial migration is a fundamental behavior that underlies the evolution of migration in general. Among fish taxa, the terminology and theory associated with partial migration has predominantly been used to describe salmon ecophenotypes, but the behavior is more widespread. Here, we ecophenotypes, but the behavior is more widespread. Here, we document partial migration for the estuarine‐dependent white perch (Morone americana), in the Patuxent River estuary (Chesapeake Bay, Maryland), wherein a portion of the population resides in freshwater natal habitats and another portion migrates down‐estuary into brackish water (salinities>3) habitats. Life‐time migration histories were examined using otolith strontium:calcium profile analysis. Alternative life history tactics, initiated during the juvenile period in response to individual physiological condition, persisted over the lifetime of the individual and had population‐level consequences, including differences in growth rate and productivity. Based upon a review of recent literature, we argue that pratical migration is more widespread among fishes than previously recognized, and such population structure has important implications for population dynamics and persistence.

The impact of fishing-induced mortality on the evolution of alternative life-history tactics in brook charr.

Although contemporary trends indicative of evolutionary change have been detected in the life-history traits of exploited populations, it is not known to what extent fishing influences the evolution of alternative life-history tactics in migratory species such as salmonids. Here, we build a model to predict the evolution of anadromy and residency in an exploited population of brook charr, Salvelinus fontinalis. Our model allows for both phenotypic plasticity and genetic change in the age and size at migration by including migration reaction norms. Using this model, we predict that fishing of anadromous individuals over the course of 100 years causes evolution in the migration reaction norm, resulting in a decrease in average probabilities of migration with increasing harvest rate. Moreover, we show that differences in natural mortalities in freshwater greatly influence the magnitude and rate of evolutionary change. The fishing-induced changes in migration predicted by our model alter population abundances and reproductive output and should be accounted for in the sustainable management of salmonids.

Analysis of Daily Growth Patterns in Young-of-Year Male Dwarf Surfperch (Embiotocidae:Micrometrus minimus) Suggests Alternative Tactics: Breed or Grow after Birth

Abstract Discontinuous variation in daily growth patterns suggests that there are alternative life-history tactics among males of a coastal fish species. Male dwarf perch are known to be mature and reproductively active at birth, exhibiting a high level of material and behavioral expenditure on breeding early in life. Males experience a substantial cost of reproduction in reduced early growth and survival relative to females. Through analysis of daily growth increments in otoliths, we showed that young-of-year males from two populations exhibit a polymorphism in daily growth patterns. A distinctive episode of narrow growth increments and slow growth punctuated the summertime growth record of some males, whereas increment widths were more uniform and growth was more rapid in other males. Discriminant function analysis revealed that features of the daily growth record varied discontinuously, falling into two distinct groups. Early-born males were more likely to exhibit the slow growth pattern, and late-born...

Delayed Dispersal and Reproduction as a Life-History Tactic in Cooperative Breeders: Fitness Calculations from Red-Cockaded Woodpeckers

The evolution of delayed dispersal and reproduction in cooperative breeders can be viewed as selection between alternative life-history tactics: (1) stay-and-foray (SAF), in which individuals delay dispersal and reproduction and compete for breeding vacancies in the vicinity of the natal territory, and (2) depart-and-search (DAS), in which individuals disperse soon after fledging to wander in search of a breeding vacancy. Using demographic data collected from red-cockaded woodpeckers (Picoides borealis), we evaluated a demographic model of the evolution of delayed dispersal and reproduction based on selection between these tactics. Because males of this species exhibit both tactics regularly, we could estimate all model parameters directly. Our estimates provide empirical support for key assumptions of demographic models of the evolution of delayed dispersal and reproduction, such as a disparity in survival between those adopting SAF and those adopting DAS during the first year of life, a low rate of successful dispersal in those practicing DAS, and low reproductive success at early ages among breeders. We show, in a population in which the fate of dispersers could be documented, that the fitness of individuals delaying dispersal and reproduction can equal or exceed that of individuals attempting early reproduction, even without indirect fitness benefits due to helping behavior.

Abandonment as a Reproductive Tactic -- The Example of Grizzly Bears

In nonexpanding or nondeclining populations in which the reproductive value of all recruits is assumed equal, life-history tactics may be compared by comparing the expected number of recruits arising from each tactic. The problem of determining the superior tactic can then be posed as a dynamic programming problem. The example of abandonment as a useful reproductive tactic in brown bears demonstrates the use of a finite state description in generating the expected number of recruits arising from a nontrivial reproductive pattern. The procedure is easily applied and is thus a powerful tool for exploring alternative life-history tactics of specific individual organisms.