Changes In Female Size Research Articles

Effects of changes in female size on relative egg production of northern shrimp stocks (Pandalus borealis)

Length is one of the main factors determining fecundity of shrimp. Therefore, changes in length distribution where larger individuals disappear from the stock may affect the relative egg production (REP) of the stock. The main objective of this study was to use fecundity of shrimp to estimate changes in REP of four inshore shrimp stocks in the period between 1990 and 2016, and estimate how changes in length at sex change ( L50) and maximum size (Lmax) impact the REP of the stocks. The results show that the REP of the shrimp stocks reduced considerably with lowering of L50 and Lmax. However, the relationship between REP and recruitment was in general poor.

ALTERNATIVE MATING STRATEGIES AND THE EVOLUTION OF SEXUAL SIZE DIMORPHISM IN THE SIDE-BLOTCHED LIZARD,UTA STANSBURIANA: A POPULATION-LEVEL COMPARATIVE ANALYSIS

Population-level comparative analyses can link microevolutionary processes within populations to macroevolutionary patterns of diversification. We used the comparative method to study the evolution of sexual size dimorphism (SSD) among populations of side-blotched lizards (Uta stansburiana). Uta stansburiana is polymorphic for different male mating and female life-history strategies in some populations, but monomorphic in others. We tested whether intrasexual selection among males, fecundity selection on females, and the presence of polymorphic strategies affected levels of SSD. We first resolved a phylogeny for 41 populations across the range of the species and documented a substantial regional structure. Our intraspecific data had significant phylogenetic signal, and correcting for phylogeny using independent contrasts had large effects on our results. Polymorphic populations had male-biased SSD and changes in male body size, levels of tail breaks, and SSD consistent with the intrasexual selection hypothesis. Monomorphic populations had changes in female size, clutch size, and SSD consistent with the fecundity selection hypothesis. Fecundity selection is a likely cause of some monomorphic populations having no SSD or female-biased SSD. Our results suggest that changes in mating strategies are associated with phenotypic diversification and multiple evolutionary forces can shape SSD.

Nesting Biology and Socially Polymorphic Behavior of the Sweat Bee <I>Halictus rubicundus</I> (Hymenoptera: Halictidae)

Halictus rubicundus Christ is a facultatively social bee demonstrating solitary behavior in regions of cool climate, social behavior in areas of warmer climate, and a mixture of social and solitary behavior in marginal environments. In this article I compare original data to those from previously published studies of H. rubicundus in a variety of environments. I describe nest structure, nest density, bee size, reproductive output, sex ratio, and incidence of predators and parasites. From the patterns that emerge, I conclude that nest-site philopatry is important in structuring populations so that social behavior is favored over bivoltinism in warm climates. The sex ratio of populations is correlated with photoperiod but the relationship is not absolute; therefore, I propose that some other causal factor or a combination of factors, such as temperature or resource availability, is involved. The same mechanism may be responsible for changes in female size during the season. Differences in social behavior do not appear to provide a barrier to reproduction, and the presence of different forms does not imply incipient speciation.

Seasonal changes in female size and its relation to reproduction in the parasitoid Asobara tabida

The relation between female size and fitness was studied in female Asobara tabida throughout the field season. The size of A. tabida females varied considerably, with average size being smallest in the middle of the season. There was a positive correlation of realized fecundity with size, and the fitness advantage of larger females increased later in the season. A possible explanation for this can be found in the energy expenditure during the season. Regression analysis showed that fat use increases with size of the female, but also with temperature. Temperature was low early and late in the season, but high in the middle. We argue that the high temperatures may constrain fitness advantages of large females because of their increased metabolic needs. Variation in the form of the fitness function within the season may moderate directional selection for larger females.

Changes in female lobster (Homarus americanus) size at maturity and implications for the lobster resource in Long Island Sound, Connecticut

Population theory predicts that, under conditions of high age/size-specific mortality rates, individuals in highly exploited populations increase their fitness by decreasing size at sexual maturity, relative to less exploited populations. The benefit of early reproductive maturation is that individuals have a higher probability of surviving to maturity and contributing progeny to maintain the population. Empirical evidence, based on morphometric data from nearly 60 000 female lobsters collected since 1981, suggests that size at sexual maturity of female lobsters in Long Island Sound (USA) has recently decreased. Our findings were supported by decreases in average size and increases in abundance of egg-bearing females over the past two decades. Changes in female size at maturity and subsequent higher egg production may also help to explain the recent increase in lobster recruitment and landings. It is unclear whether these changes were caused by density-dependent factors related to the high exploitation of the species, by natural environmental factors (e.g. higher seawater temperatures), or a combination of the two.

CHARACTER DISPLACEMENT AND RELEASE IN THE SMALL INDIAN MONGOOSE,HERPESTES JAVANICUS

In western parts of its native range, the small Indian mongoose (Herpestes javanicus) is sympatric with one or both of two slightly larger congeners. In the eastern part of its range, these species are absent. The small Indian mongoose was introduced, about a century ago, to the West Indies, the Hawaiian islands, Mauritius, the Fijian islands, and Okinawa. All introductions except possibly that to Mauritius were from the region of Calcutta and Bangladesh, where it is sympatric with both congeners. No other mongoose is present on any of these islands. In each instance, the introduced population derived from a small propagule. We examined size variation in the maximum diameter of the upper canine tooth (the prey-killing organ) and skull length. In the eastern (allopatric) part of its native range, males of the small Indian mongoose are much larger in both traits than in the western (sympatric) regions, approaching the size of the smaller of its absent two congeners, Herpestes edwardsii. Females from the allopatric part of the range are also larger than those of the source region. The species is more sexually dimorphic in the region of allopatry. On all islands to which it has been introduced, in 100–200 generations the small Indian mongoose has increased in male size and in sexual dimorphism; changes in female size have been slight and inconsistent. In general, sizes of island individuals are approximately intermediate in size between those in the region of origin (where they are sympatric and small) and those in the region of allopatry. Sexual dimorphism is greatest for canine diameter. Thus, H. javanicus shows variation consistent with ecological release from competition with its congeners. There is no evidence on whether this variation is genetic, nor on what dietary items might be partitioned between species and between sexes. However, morphological variation is consistently smaller for both traits and both sexes on the islands of introduction than in any part of the native range, consistent with idea of a genetic bottleneck imposed by the small propagule size. Neither of the two congeneric mongooses shows morphological variation consistent with ecological release from competition with H. javanicus in the southern part of their ranges, where the latter species is absent.

Effects of water quality on the vector competence of Culex tarsalis (Diptera: Culicidae) for western equine encephalomyelitis (Togaviridae) and St. Louis encephalitis (Flaviviridae) viruses.

The effects of water quality during immature development on the vector competence of adult female Culex tarsalis Coquillett for western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses was evaluated during 6 field and 4 laboratory experiments. Immatures of the Bakersfield Field Station laboratory strain and the F1 progeny of field-collected females were reared in the field or laboratory and then infected by feeding on pledgets, after which remnants (head, thorax, abdomen), legs, and salivary secretions were tested for WEE or SLE virus to estimate infection, dissemination, and transmission rates, respectively. Although the salt content of the 6 larval habitats varied markedly (range, alkalinity 160-1,310 ppm CaCO3, conductivity 460-7,600 microns hos/cm, chlorides 22-1,560 ppm) and significantly altered immature survival, development time, and female body size (wing length), consistent changes in infection, dissemination, or transmission rates were not observed. Susceptibility (ID50) to WEE virus in field strains decreased as a linear function of developmental time, with populations from a dry alkali lake bed (Goose Lake) least susceptible. Three subsequent laboratory experiments that tested the effects of rearing immatures in dilution series of water from Goose Lake failed to produce consistent within or among experiment patterns in vector competence. A 4th laboratory experiment tested changes in NaCl concentration with negative results. Changes in female size was not related to vector competence. These and previous temperature studies indicated that temporal changes in vector competence observed within and among field populations probably were related to intrinsic genetic factors and were not related directly to extrinsic factors in the immature aquatic environment.