Rate Of Offspring Production Research Articles

Influence of female reproductive anatomy on the outcome of sperm competition in Drosophila melanogaster.

Females as well as males can influence the outcome of sperm competition, and may do so through the anatomy of their reproductive tracts. Female Drosophila melanogaster store sperm in two morphologically distinct organs: a single seminal receptacle and, normally, two spermathecae. These organs have different temporal roles in sperm storage. To examine the association between sperm storage organ morphology and sperm competition, we used a mutant type of female with three spermathecae. Although the common measure of sperm competition, P(2), did not differ between females with two and three spermathecae, the pattern of sperm use over time indicated that female morphology did affect male reproductive success. The rate of offspring production by females with three spermathecae rose and fell more rapidly than by females with two spermathecae. If females remate or die before using up second male sperm, then second male reproductive success will be higher when they mate with females with three spermathecae. The results indicate that temporal patterns of sperm use as well as P(2) should be taken into account when measuring the outcome of sperm competition.

Litter Overlap in Gambusia hubbsi: Superfetation Revisited

The frequency of litter overlap, the simultaneous presence of two litters at different stages of development within a single female, varies among populations of Gambusia hubbsi in different habitats on Andros, Bahamas. In freshwater bluehole and shallow water populations, less than 2% of the females carried two litters, independent of the difference in developmental stage between the litters. In well field populations, 2% of the females carried two litters composed of immature and mature oocytes, whereas 10% carried developing oocytes and late stage embryos, and 16% carried mature oocytes (or older) and late stage embryos. Among females from populations that we introduced into unoccupied well fields 2% carried two litters composed of immature and mature oocytes, about 14% carried developing oocytes and late stage embryos, and less than 6% carried mature oocytes (or older) and late stage embryos. When two litters composed developing oocytes and late stage embryos were present, the two litters were of equal size, and the total number of offspring was 1.5 times larger than expected on the basis of female body length. When two litters composed mature oocytes (or older stages) and late stage embryos were present, the two litters were also of equal size, and the total number of offspring was as expected on the basis of female body length. Litter overlap was independent of female size. A comparison of the consequences of litter overlap for strictly lecithotrophic and strictly matrotrophic modes of reproduction with the patterns of litter overlap observed in G. hubbsi, suggests that litter overlap in G. hubbsi reduces the cost of reproduction, but does not increase the rate of offspring production.

Host specificity and comparative foraging behaviour of Aenasius vexans and Acerophagus coccois, two endo‐parasitoids of the cassava mealybug

AbstractTwo encyrtid parasitoids, Aenasius vexans Kerrich (Hymenoptera: Encyrtidae) and Acerophagus coccois Smith (Hymenoptera: Encyrtidae), were compared for their degree of dietary specialisation and the impact this has on their foraging strategies. Both parasitoid species are significant for biological control of the cassava mealybug, Phenacoccus herreni, Cox & Williams (Homoptera: Sternorrhyncha) a major Latin American pest of cassava, Manihot esculenta Crantz, an important root crop. Host acceptance and parasitism were analysed in seven mealybug species (with different levels of polyphagy) occurring in and around cassava fields. Results demonstrate that, in this ecosystem, An. vexans is a specialist for P. herreni while Ac. coccois is a generalist on the first and second trophic level. Of the seven mealybug species, P. herreni and P. madeirensis Green were the most acceptable hosts for Ac. coccois, followed by Ferrisia virgata Cockerell. Ac. coccois did not accept the other four mealybug species.The foraging and oviposition behaviour of individual parasitoids was observed in bioassays with cassava leaves infested by P. herreni. The two species used different strategies to locate their host. Aenasius vexans spent significantly more time walking and standing on an infested leaf and examined a host longer than did Ac. coccois. Acerophagus coccois, in contrast, spent more time for oviposition. As a consequence An. vexans parasitised more hosts in a given time than did Ac. coccois. Because the rate of offspring production of the two species did not differ, we conclude that the gregarious Ac. coccois's strategy to deposit several eggs at once might compensate for its relatively low number of ovipostitions, compared with the solitary An. vexans. These findings suggest that, given the advantages and limitations of each species, a multi‐species approach to biological control of P. herreni may yield best results.

Asymptotic Behavior of an Age-Structured Population Model and Optimal Maturation Age

A continuous age-structured population model with two population groups, juveniles and adults, and with a dynamics for the resource, is considered. The only density dependence is through a uniform increase of the death rates. A complete description of the asymptotic behavior of the population dynamics system is obtained showing under natural hypotheses the existence of a nontrivial (“ecological”) equilibrium which attracts any initial nonzero population with nonzero initial amount of resources. Assuming that the offspring production rate is an increasing function of the maturation age, the evolutionarily stable value of this variable is briefly discussed.

Gender preselection in cattle with intracytoplasmically injected, flow cytometrically sorted sperm heads.

We investigated the development to the blastocyst and subsequent live-offspring stages of in vitro-matured bovine oocytes intracytoplasmically injected with flow cytometrically sorted bull sperm heads. Bull sperm heads, prepared by ultrasound sonication, were distinguished and sorted on the basis of their relative DNA contents using a flow cytometer/cell sorter modified for sorting sperm. By fluorescence in situ hybridization, the proportion of sperm confirmed as having Y specific DNA in the fraction sorted for the Y sperm was 82%. Injection with single sorted sperm heads of in vitro-matured oocytes (cultured for 24 h) resulted in 46.6% cleavage and 6.9% blastocyst development rates. Embryo transfer of 48 blastocysts (Days 7-8) to recipients (one per recipient) resulted in 20.8% pregnancy and 20.8% normal live offspring production rates. The birth of 8 male and 2 female calves represents an 80% sex preselection accuracy rate.

Criteria of reproductive success.

To determine reproductive success, it is necessary for the researcher to specify a criterion of success, such as the number of a parent's offspring living to the age of reproduction. A measurement model, which includes the researcher's choice of criterion, has been proposed to estimate the lifetime reproductive success (R) of long-lived animals from complete or incomplete knowledge of the reproductive life histories of mothers and the survival fates of offspring. This research uses R and data from female baboons of Mikumi National Park, Tanzania, as vehicles to investigate the relationship between reproductive success and several criteria. Secondarily, it also investigates the relationship between R and the number and rate of offspring production. Seven criteria of reproductive success, ranging in 12-month increments form 0 (birth) to 72 months of offspring life, were applied to 10.5 years of reproductive data from 61 Mikumi females. Theoretically, the best scenario for comparative purposes is an invariant R across different criteria; however, the mean R systematically increased as the criteria increased. This is more an inconvenience than a serious problem because high correlations indicate high predictability between Rs from pairs of criteria. R was modestly correlated with the rate of offspring production, indicating that rate can be employed as a rough index of reproductive success. The choice of a criterion is a trade off between theory, practicality, the strength of the criterion, and the effect of the choice upon sample representativeness and size.

Interspecific interference betweenApoanagyrus lopeziandA. diversicornis, parasitoids of the cassava mealybugPhenacoccus manihoti

AbstractThe parasitoidsApoanagyrus lopeziDe Santis andA. diversicornis(Howard) (Hymenoptera: Encyrtidae) have been introduced into Africa for the biological control of the cassava mealybugPhenacoccus manihotiMatile‐Ferrero (Homoptera: Pseudococcidae). We have studied competition between these species to investigate if they can coexist. Here we report on the influence of the simultaneous presence of non‐conspecific adult females on searching efficiency on patches. Wasps of either species foraged on discs of cassava leaf with mealybugs, while at the same time different numbers of non‐conspecifics were also depleting the patch. Patch area per parasitoid and number of hosts available to each parasitoid were equal in all treatments.In both species, the presence of other foragers clearly affected several aspects of the parasitoids' behaviour. Patch residence time increased with the number of non‐conspecifics inA. diversicornis.In both parasitoid species, the proportion of hosts left unparasitized after the patch visit decreased with increasing numbers of females on the patch. The proportions of super‐ and multiparasitism did not change with the number of females. Both species produced more offspring during a patch visit in the presence of more non‐conspecifics. These behavioural changes did not, however, lead to a change in the offspring production rate on patches.A. diversicornisproduced offspring at a rate three times that ofA. lopeziwhen oneA. lopeziand oneA. diversicornisforaged simultaneously. This is the first report of an aspect of interspecific competition whereA. diversicornishas an advantage overA. lopezi.Interference between adult females thus promotes coexistence of the two species onP. manihoti.

Metabolic Rates and Life Histories in Birds

It has been argued that metabolic rate is an important variable in the evolution of lifehistory variation: high metabolic rates relative to body size are associated with high fecundity and short life-spans. We present here the first analysis in birds of the relationship between life-history variation and metabolic rate, controlling for the effects of body size. Our results from 325 species belonging to 18 different orders do not support the prediction that metabolic rate is positively correlated with the rate of offspring production and neonatal growth. Further, no evidence is found for the predicted negative association between metabolic rate and life-span. We conclude that there is no empirical evidence, based on the available data, that metabolic rate differences are associated with life-history variation in birds independently of body weight and phylogenetic association. Key-words: Birds, comparative study, life-history variation, metabolic rate

Testing Theories of Clutch Overlap with the Reproductive Ecology of Heterandria Formosa

We used laboratory and field studies of the reproductive ecology of the poeciliid fish Heterandria formosa to examine the possible mechanisms that have driven the evolution of superfetation (simultaneous provision of maternal care to sets of dependent offspring in diverse stages of development). Increased food levels in the laboratory increased the number of broods that a female produced by increasing the level of superfetation. Brood sizes were determined by female body size and were unaffected by food level. Offspring size was unaffected by food level but varied with female age. Different females had different age—specific offspring sizes. Brood size and offspring size were not correlated, even when female size was held apart. In the field the level of superfetation increased with the total number of embryos, even when female size was held apart. Larger, older females displayed higher levels of superfetation than smaller, younger females. Superfetation appeared to increase offspring production rate without compromising brood size or individual offspring size. The correlations among reproductive traits that were displayed by H. formosa were quite different from those found in poeciliid fish without superfetation. Heterandria exhibited a demographic regime characterized by overlapping generations but high adult mortality rates relative to juvenile mortality. We used these results to test three general hypotheses for the evolution of clutch overlap. The results support Burley's (1980) hypothesis that clutch overlap is an adaptation to maximize offspring production rate in the face of limited maternal effort. We modified this hypothesis to specify production of large offspring. In poeciliids, the critical tests of this modification will involve comparing the reproductive and demographic patterns observed in species such as Heterandria formosa, which occupies an extreme position with regard to clutch overlap, with species such as Gambusia affinis, which does not display clutch overlap, yet is often syntopic with Heterandria. Similar comparative studies in demography could address the question of why clutch overlap is not more common.