Selection For Life-history Traits Research Articles

Life history buffering in Antarctic mammals and birds against changing patterns of climate and environmental variation

AbstractThe consequences of warming for Antarctic long‐lived organisms depend on their ability to survive changing patterns of climate and environmental variation. Among birds and mammals of different Antarctic regions, including emperor penguins, snow petrels, southern fulmars, Antarctic fur seals and Weddell seals, we found strong support for selection of life history traits that reduce interannual variation in fitness. These species maximize fitness by keeping a low interannual variance in the survival of adults and in their propensity to breed annually, which are the vital rates that influence most the variability in population growth rate (λ). All these species have been able to buffer these rates against the effects of recent climate‐driven habitat changes except for Antarctic fur seals, in the Southwest Atlantic. In this region of the Southern Ocean, the rapid increase in ecosystem fluctuation, associated with increasing climate variability observed since 1990, has limited and rendered less predictable the main fur seal food supply, Antarctic krill. This has increased the fitness costs of breeding for females, causing significant short‐term changes in population structure through mortality and low breeding output. Changes occur now with a frequency higher than the mean female fur seal generation time, and therefore are likely to limit their adaptive response. Fur seals are more likely to rely on phenotypic plasticity to cope with short‐term changes in order to maximize individual fitness. With more frequent extreme climatic events driving more frequent ecosystem fluctuation, the repercussions for life histories in many Antarctic birds and mammals are likely to increase, particularly at regional scales. In species with less flexible life histories that are more constrained by fluctuation in their critical habitats, like sea‐ice, this may cause demographic changes, population compensation and changes in distribution, as already observed in penguin species living in the Antarctic Peninsula and adjacent islands.

Discrete genetic variation in mate choice and a condition-dependent preference function in the side-blotched lizard: implications for the formation and maintenance of coadapted gene complexes

Variation in female preference functions, both genotypic and phenotypic, has been largely ignored in the literature, despite its implications to the maintenance of genetic variation in populations and the resolution of the ‘‘Lek paradox.’’ Polymorphic populations, such as in the side-blotched lizard, provide ideal study systems for its investigation, especially in the context of incipient processes of sympatric speciation. Females of the side blotch lizard exist in 2 genetically distinct morphs, yellow throated and orange throated, that experience disruptive selection for life history traits. Males express 3 throat color morphs, blue, orange, and yellow, that exhibit alternative strategies in intrasexual competition. We experimentally tested for female preference in triadic mate choice trials to identify the presence of discrete genetic and condition-dependent variation in female preference function. We found that females did in fact show genetic variation in preference for males but that females also operate a multicondition preference function dependent upon the genotype of the female and her state (number of clutches laid). Females exhibited positive assortative mating prior to the first clutch. However, prior to later clutches, orange females switched choice, preferring yellow males. These findings are discussed in relation to the maintenance of coadapted gene complexes within populations and the prevention of divergent directional selection (population bifurcation) by conditiondependent variation in mate choice. Key words: coadapted gene complex, condition dependent, disruptive selection, genetic variation, lek paradox, mate choice, polymorphism, side-blotched lizard, sympatric speciation. [Behav Ecol]

Sperm Competition in Salmon Hatcheries: The Need to Institutionalize Genetically Benign Spawning Protocols

Abstract Salmon hatcheries in the Pacific Northwest historically spawned adults by combining eggs from several females and milt from several males in a single container. This mixed-milt approach leads to significant sperm competition and highly unequal genetic contributions from male spawners. Sperm competition substantially reduces the genetic effective number of breeders (Nb ) relative to the actual number of spawners (Ns ). Sperm competition in vitro can also result in undesirable artificial selection for life history traits (e.g., age or size at maturity) that are correlated phenotypically with sperm potency and fertilization success. A large number of salmon hatcheries in the Pacific Northwest, particularly those within some state agencies, continue to use mixed-milt fertilization despite documented genetic effects and potential risks. The continued use of mixed-milt fertilization may be due, in part, to insufficient genetic oversight of hatchery operations. As a general rule, salmon hatcheries shoul...

Pleiotropic effect, clock genes, and reproductive isolation

AbstractThe mechanism by which a clock gene pleiotropically controlling life history and behavioral traits causes reproductive isolation is explained using a model species, the melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). Melon flies mate once a day, at dusk. The population selected for life history traits exhibits correlated responses in the time of mating during the day. For example, the fly populations selected for faster (slower) development have an earlier (later) time of mating. A circadian rhythm controls the time of mating. The circadian periods in constant darkness were about 22 h in lines selected for a short developmental period and about 31 h in lines selected for a long developmental period. The data on crosses between the selected lines indicated that the developmental period is controlled by a polygene, whereas the circadian period may be controlled by a single clock gene. These results suggest a clock gene pleiotropically controls developmental and circadian periods in the melon fly. Reproductive isolation may often evolve as an indirect (pleiotropic) consequence of adaptation to different environments or habitats. For example, niches that are temporally or seasonally offset can select organisms with different developmental characteristics. These developmental differences can inadvertently cause reproductive isolation by a variety of means including shifts in mating activity patterns. The difference in time of mating between populations selected for developmental period translated into significant prezygotic isolation, as measured by mate choice tests. If the mating time between populations differed more than 1 h, the isolation index was significantly higher than zero. These findings indicate that premating isolation can be established by a pleiotropic effect of a clock gene. There are many examples in which the difference in timing of reproduction prevents gene flow between populations, such as the egg spawning time in marine organisms, the flowering time in angiosperms, and the time of mating in insects. In such organisms, if genetic correlations between circadian rhythm and reproductive traits exist, multifarious divergent selection for life history traits would often accelerate the evolution of reproductive isolation through clock genes. Natural populations may diverge in reproduction time through drift, direct natural selection for time of reproduction, or as a by‐product effect of genetic correlations. In any case, clock genes are keys in reproductive isolation.

The Maturity Index,the evolution of nematode life history traits, adaptive radiation and cp-scaling

Nematodes are increasingly being used in environmental studies. One of the potential parameters to measure the impact of disturbances and to monitor changes in structure and functioning of the below-ground ecosystem is the nematode Maturity Index; an index based on the proportion of colonizers (r-strategists s.l.) and persisters (K-strategists s.l.) in samples. In this paper the original allocation of nematode taxa on the colonizer-persister scale, and the tolerance and sensitivity of colonizers and persisters are discussed from an evolutionary viewpoint. The phenomenon that neither relative egg size nor body length is an unequivocal character to scale nematodes suggests that the main selection for life history traits occurred independently in the major evolutionary branches.

Evolution of yields from populations with age-specific cropping

Age-specific exploitation of a natural population acts as a selective force on genetic variation in life history traits. Evolution arising from this selection may bring about evolutionary changes in the total yield which the population is able to sustain. An analysis of this process is given for a harvested population with densitydependent recruitment, in which selection of life history traits by cropping is independent of density and frequency. Evolution of the total yield depends on an interplay between the yield from an individual over the course of its life and recruitment; whether the total yield increases or decreases depends on the properties of particular populations. Evolution brought about by harvesting does not, in general, lead to the maximization of the total yield. Nonetheless, by appropriate choice of an age-specific harvest pattern, it is possible in principle to select the life history which gives the maximum total yield following evolution; this harvest pattern is called the ‘evolutionarily stable optimal harvesting strategy’ (ESOHS). Results of the analysis are illustrated with data on the Arcto-Norwegian cod.