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PubMed1992

Reproductive activity of Synosternus cleopatrae (Siphonaptera: Pulicidae) in relation to host factors.

Reproductive activity of Synosternus cleopatrae (Rothschild) infesting Gerbillus andersoni allenbyi Thomas was studied in a natural setting in Israel. Rodents were trapped and measured (weight and length), their sex was identified, and their reproductive status estimated. Their ectoparasites were removed, and fleas were dissected and their oocytes measured. Two indices of flea reproductive activity were analyzed: "reproductive status," which distinguished between gravid and nongravid females, and "reproductive intensity," which was estimated as the sum over the two largest oocytes of the products of oocyte length multiplied by oocyte width. Both indices showed that no reproduction took place between November and January, but reproduction was relatively stable during the rest of the year. Although flea reproductive activity differed significantly among individual hosts, only a small fraction of gerbils (10-15%) carried a significantly different proportion of reproductive fleas than their monthly sample proportion (based on all fleas regardless of hosts). All these hosts carried a lower proportion of reproductive fleas than their monthly sample proportion. The host's sex, but not reproductive status or age, had a significant effect on flea reproduction, expressed as a higher reproductive activity on male gerbils. Infestation burden expressed as ectoparasite counts was included in the statistical analysis. Only lice, Polyplax gerbilli Ferris, but not S. cleopatrae, Stenoponia tripectinata (Tiraboschi), and a total of five mesostigmatid Acari had a significantly negative association with S. cleopatrae reproductive activity. These relationships between S. cleopatrae reproductive activity and the host infestation burden do not support the hypothesis of modulation of S. cleopatrae reproduction by the infestation burden. However, differences in the reproductive activity of ectoparasites between their hosts may play a major role to generate the parasite clumped distribution. Thus, gerbil males probably carry more fleas than gerbil females because of the higher reproductive activity of S. cleopatrae on gerbil males.

Animals↗
PubMed1992

Environmental cues, endocrine factors, and reproductive diapause in male insects.

Environmental cues, mostly photoperiod and temperature, mediated by effects on the neuroendocrine system, control reproductive diapause in female insects. Arrest of oocyte development characterizes female reproductive diapause, which has two major adaptive functions: It improves chances of survival during unfavorable season(s), and/or it confines oviposition to that period of the year that is optimal for survival of the eggs and progeny. Although reproductive diapause is less well studied in male insects, there may be no sex-dependent differences in regard to the first of these functions. The second one, however, is not valid for the male; instead, selection pressure directs the male's reproductive strategy toward maximum chances of fertilization of the female's eggs with minimum waste of energy. Therefore, in species with female reproductive diapause, the males may or may not exhibit diapause, but if they do, their diapause must be adapted to that existing in conspecific females. Male reproductive diapause is defined as a reversible state of inability of the male to inseminate receptive females. In relation to reproductive diapause, there are several patterns of coadaptations between male reproductive strategy and timing of female receptivity. (a) In some insects, the females are receptive in the early part of their diapause; mating occurs during this period and there is no diapause in the male. The male dies shortly after copulation and the female stores the sperms to fertilize the eggs that develop after termination of the female's diapause. (b) In some species, as in the grasshopper Anacridium aegyptium, females are receptive during diapause; though oocyte development is arrested, copulation occurs and the stored sperms fertilize the eggs when the female's diapause ends. Males were claimed to have no diapause, but recent studies have revealed the presence of a reproductive diapause in a proportion of the males. This and other cases show that female receptivity during reproductive diapause may or may not be accompanied by male reproductive diapause. If there is a reproductive diapause in the male, it is controlled by the same endocrine mechanism, the corpora allata (CA), as in the females. (c) In many species females are refractory during their diapause. In these cases, males exhibit reproductive diapause, which may be light, as in the beetle Oulema melanopus, or well established, as in certain grasshoppers, butterflies, and beetles. In the latter cases, male diapause is controlled by similar environmental cues (photoperiod, temperature) and by the same intrinsic mechanism (neuroendocrine system, especially CA) as female diapause.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1992

Does seasonal reproductive state affect the neuroendocrine response of the ewe to a long-day pattern of melatonin?

This study examined whether or not the reproductive response of female sheep to photoperiod varies with seasonal reproductive state. The specific objective was to test the hypothesis that the reproductive response to a long-day pattern of melatonin varies with the reproductive state of the ewe. The response examined was the synchronization of reproductive neuroendocrine induction (rise in serum luteinizing hormone, or LH) following nocturnal infusion of melatonin into pinealectomized ewes for 35 consecutive nights. This infusion restored a pattern of circulating melatonin similar to that in pineal-intact ewes maintained in a long photoperiod (LD 16:8). The ewes had been pinealectomized and without melatonin replacement for 16-25 months prior to the study. They were in differing reproductive states at the start of the infusion, as their endogenous reproductive rhythm had become desynchronized among individuals and with respect to time of year. Noninfused pinealectomized ewes served as controls. Regardless of the reproductive state at the start of the 35-day infusion of the long-day pattern of melatonin, all treated ewes exhibited the same reproductive neuroendocrine response after the infusion was ended. This consisted of a synchronized rise in LH some 6-8 weeks after the infusion was terminated, the maintenance of a high level of serum LH for some 15 weeks, and a subsequent precipitous fall in LH to a very low level. These results provide evidence that a long-day pattern of melatonin can synchronize reproductive neuroendocrine induction in the ewe, regardless of reproductive condition, and thus do not support the hypothesis that this response differs with seasonal reproductive state.

Animals↗