The Influence of Somatic Investment on the Patterns of Reproduction in POECILIA LATIPINNA (Pisces: POECILIIDAE)

In Poecilia latipinna size-specific reproductive and survivorship patterns were correlated with changes in habitat availability. Of the numerous physical, chemical, and biological parameters associated with a reduction in available habitat, probably the most important was reduced food availability. Large (old) females, theoretically with a low reproductive value, allocated energy to reproduction regardless of habitat and, presumably, food availability. When reproductive activities were initiated in March, habitat availability was modest. In association with a severe reduction in available habitat in April, large females were subject to a substantial loss of body weight during the yolk-loading phase of the reproductive cycle. This loss, primarily of somatic tissue, was very costly and heavy mortality ensued. Habitat availability increased during late May and June and survivorship increased. By August the somatic condition of large females had improved significantly. As in April, yolk-leading resulted in a loss of body weight; however, the loss consisted of approximately 70% lipid. Although the cost was lower than April, the necessity of subsidizing reproduction with somatic tissue may account for the slight reduction in survivorship observed in September. Smaller (younger) females, theoretically with a higher reproductive value, allocated energy to reproduction in response to increases in habitat, and presumably food availability. This response was in the form of an increased number of small reproducing females and was not evident until the month following the increase in available habitat. In contrast to large females, reproductive activities among small females were initiated in April. In association with a severe reduction in habitat availability, small females were subject to a loss of dry weight during yolk-loading, which consisted of approximately 44% lipid. The cost of reproduction was reduced and survivorship improved relative to the large females. Despite an increase in available habitat in June, small females curtailed reproduction in favor of survival and increased fecundity afforded by a greater body size. By early August an increase in reproductive activities was evident among small females. The somatic condition of these females was significantly improved in comparison to April females. In contrast to large August females, small females did not subsidize reproduction with somatic tissue. The change in body weight was attributable to a loss of lipid. By early September the available habitat had increased dramatically. In comparison to August, the high number of small reproducing females suggested the response to improved conditions may be rapid. Changes in food availability and, thus the total energy budget (lower in spring, higher in the summer and fall) and the associated cost of reproduction (higher in spring, lower in fall) from April to September were not reflected by changes in fecundity. It appeared that under the conditions that prevailed during this study, a female that made a commitment to reproduction produced a size-specific brood of a fixed quality regardless of food availability and reproduction cost. If a female was able to assimilate excess energy during the gestation period, that energy was allocated in maintenance (i.e. repaying any somatic debt) and growth

Sex-Ratio In The Sailfin Molly, Poecilia-Latipinna

R. A. Fisher\u27s theory predicts that the sex ratio at conception and birth should be 1.1 in most diploid, bisexual organisms. This ratio should not be directly influenced by differential mortality or other factors acting to bias sex ratios away from 1.1 among adults. Most live-bearing fishes of the family Poeciliidae exhibit female-dominated adult sex ratios. The sex ratios among young and juveniles are well-known for only one species, Gambusia affinis. For this species, the secondary sex ratio is 1.1, but females predominate among adults. We examined sex ratios in the sailfin molly, Poecilia latipinna, on the east-central coast of Florida. The sex ratio at birth was examined in lab-reared broods. Sex ratios among juveniles and adults were recorded from two populations sampled monthly for two years. The sex ratio was not significantly different from 1.1 in 22 of the 26 broods reared. In four broods, females predominated significantly. Overall, 291 of 568 neonates (51.2%) were females. Apparently, the sex ratio in a small number of broods may depart significantly from unity; but among all neonates in a cohort, the sex ratio is very near 1.1. In field populations, the sex ratio among small (juvenile) mollies was not significantly different from 1:1 in 32 of 47 monthly samples. In samples where departure was significant, there was no clear temporal or spatial pattern and no clear explanation for the direction or degree of skewness. Overall, females constituted 47-54% of about 10,000 small fish examined. Except for January, 1974, at RRCD, the sex ratio among adults from field samples was highly skewed in favor of females at both study sites. The departure from 1:1 was statistically significant in 44 of 46 cases. Overall, 72% of over 17,000 adult fish were females. In some months females constituted 80-90% of the adult fish captured. Our results support Fisher\u27s theory. Despite highly skewed sex ratios in adults, males and females occur in approximately equal numbers among young and juveniles. Differential mortality of males appears to coincide with the initiation of sexual maturation. Several proximate causes of differential mortality have been suggested. Ultimately, differential male mortality must be adaptive since it seems to be a general phenomenon in the family Poeciliidae. We discuss the significance of unbalanced sex ratios in poeciliid reproductive systems and suggest two alternative hypotheses for how skewed ratios may have evolved

The Relationship Between Interbrood Interval And Yolk Loading In A Generalized Poeciliid Fish, Poecilia-Latipinna

Interbrood intervals in the livebearing sailfin molly, Poecilia latipinna, were studied in laboratory experiments. Of the factors investigated, temperature was the most important in influencing interval length, with shorter intervals characteristic of females maintained at higher temperatures. However, even when temperature and food level were controlled, there was significant variation in interbrood interval. Pooled data from five experiments gave a non-normal distribution of intervals ranging from 26-50 d, with a mode of 33 and positive skewness. The results of a subsequent yolk-loading experiment conformed intuitively and statistically with the results of the interbrood interval studies, suggesting that most of the variation in interval length is explained by variation in the vitellogenic phase of the ovarian cycle. Most females completed egg maturation and fertilization 4-8 d after parturition, when the eggs had reached about 2.2 mm diameter. However, some females exhibited accelerated egg maturation while others were dramatically retarded. Females that are in poor condition following parturition appear to be slow in yolking the next clutch of eggs and, therefore, will have longer interbrood intervals. Interspecific comparisons reveal consistent differences in interbrood interval among some generalized poeciliids. Differences between the sailfin molly and the guppy, P. reticulata, are maintained across a broad temperature range. However, it is unclear whether the distinctions are due to differences in the yolk-loading period, the gestation period, or both. In general, species that are larger at birth have longer interbrood intervals

Challenges and solutions for clinical development of new antibacterial agents: Results of a survey among pharmaceutical industry professionals

As the number of antibacterial medicines in the pipeline remains low, we anonymously surveyed pharmaceutical industry professionals on challenges and solutions for clinical development of these agents. Challenges were reported primarily as financial and regulatory. For multi-drug resistant organisms, there are needs for rapid diagnostic tests, new regulatory guidance, and adaptation of endpoints/trial designs. Regulators and public-private initiatives are addressing these challenges, to help ensuring that proposed solutions have the support of all involved stakeholders

Correction to: The role of hybridisation in the origin and evolutionary persistence of vertebrate parthenogens: a case study of Darevskia lizards.

An amendment to this paper has been published and can be accessed via a link at the top of the paper