Menstrual-cycle phase and sexual behavior in semi-free-ranging stumptail macaques (Macaca arctoides)

The sexual behavior and female reproductive cycles of a group of island-dwelling stumptail macaques (Macaca arctoides)were monitored over a 6-month period, yielding 530 observation hr and 268 copulations. Compared to nondominant males, the dominant male copulated at a relatively high rate throughout the cycle, but largely with one high-ranking female. The non-dominant males copulated most frequently at midcycle. Female presenting was highest at midcycle, but only to the dominant male. Cross-study discrepancies may be due to different observation methods and restricted environmental conditions that mask female-initiated sexual behavior. The more naturalistic setting of this study allowed for a fuller expression of proceptivity. Contrary to some previous conclusions, present findings suggest that both hormonal and socioenvironmental factors influence the patterns of sexual behavior found in stumptail macaque colonies.     

Patterns of variation in tail ornament size in birds

In recent years several different kinds of sexual selection models have been developed, and tail ornaments in birds have frequently been used as an example of a sexually selected character where the models might apply. However, very little is known about intra- and interpopulation variation in ornament size. We have studied the elongated tail ornaments in four species of whydahs Vidua , the forktailed flycatcher Tyrannus savana and the Asian paradise flycatcher Terpsiphone paradisi. Ornaments were relatively longer in males with the longest tarsi ('heterogony' with positive allometry). Also, tail lengths were remarkably variable within each geographical area, the coefficient of variation (average = 11%) being three times as high as for body size characters. Models, with female preference of ornaments bearing no relation to male viability, usually generate lines of neutral equilibria. Thus, they predict extraordinary variation in ornaments between populations. However, elongated tail ornaments did not show higher geographical variation than the body size characters, suggesting that there is no line of equilibria for these ornaments.     

Effects of early adult experience on host selection in insects: Some experimental and theoretical results

A field experiment with Drosophila melanogasterrevealed that when flies encounter a particular food type soon after emergence, the probability of their subsequently being attracted to such a resource is increased. In this experiment, the length of time flies experienced their postemergence environments was under the control of the flies themselves. The experiment thus realistically mimicked one form of experiential effect that may be important in nature. A theoretical model is developed which shows that enhanced adult preferences for the types of resources fed on as larvae can substantially increase the degree of host-based genetic subdivision within a polyphagous population.     

The Tangled Bank: The maintenance of sexual reproduction through competitive interactions

The maintenance of sexual reproduction is discussed using a model based on the familiar Lotka-Volterra competition equations. Both the equilibrium and the stability conditions that allow a sexual population to resist invasion by a single asexual clone are considered. The equilibrium conditions give results similar to previous models: When the cost of sex, within phenotype niche width, and environmental variance are low, the sexual population coexists with the asexual clone and remains at a high density. However, the asexual clone is never completely excluded. Analysis of the stability conditions shows a different picture: The introduction of an asexual clone considerably reduces the stability of the community. However, owing to its larger total niche width, the sexual population exists partly in a “competitor-free space” where the asexual clone has almost no influence on the outcome of the interactions. Therefore the asexual clone is less stable than the sexual population and has a higher probability of extinction. In contrast, the sexual population does not become extinct, since the extreme phenotypes remain at a stable, though low, density, and the central phenotypes, where stability is low, are recreated every generation through recombination. I therefore conclude that the ecological conditions under which sexual reproduction is favored over asexual reproduction are fairly easily attained and are more general than previous analyses had suggested.     

Prey selectivity inEuseius tularensis [Acari: Phytoseiidae]

Differences in responsiveness to potential prey and pollen were tested in the facultative predator,Euseius tularensis Congdon. Following isolation without food for 16 h, adult female mites were observed with one of the following potential foods: pollen ofMalephora crocea (Jacquin) Schwantes,Scirtothrips citri (Moulton) 2nd instar larvae,Tetranychus pacificus McGregor nymphs and ♂,Panonychus citri (McGregor) nymphs and ♂,E. hibisci (Chant) larvae, andE. tularensis larvae. Responses were compared using the proportion of encounters that resulted in consumption. This proportion was highest when pollen was encountered, followed byS. citri andT. pacificus. Consumption was much lower in response toP. citri and congeneric larvae. WhenS. citri larvae were encountered a 2nd time, 1 to 2 h after the initial capture and consumption, responsiveness increased to a level equal to the response observed with pollen. These results suggest thatE. tularensis is a more effective biological control agent of citrus thrips (S. citri) than of citrus red mite (P. citri).     

The influence of prior ovipositional experience on host selection in four species of aphidiid wasps (Hymenoptera: Aphidiidae)

We evaluated the influence of prior ovipositional experience on host selection in four solitary parasitoids, Aphidius erviHaliday, A. pisivorusSmith, A. smithiSharma & Subba Rao, and Praon pequodorumViereck (Hymenoptera: Aphidiidae). When provided simultaneously with equal numbers of two species of aphids, Acyrthosiphon pisum(Harris) and Macrosiphum creeliiDavis (Homoptera: Aphididae), all four parasitoids showed a moderate to strong preference for A. pisum.This preference did not increase after sampling, except in P. pequodorum.Learning did not alter host selection behavior in A. erviand P. pequodorum.However, females of A. pisivorusconditioned on A. pisumselected fewer M. creeliithan unconditioned wasps and wasps conditioned on M. creelii.It is suggested that prior ovipositional experience influences a parasitoid's expectations of the kinds of hosts available, but it does not alter the (innate) rank order of hosts.     

Sex determination and differentiation in organisms other than higher plants

The understanding of sex determination in general, but in particular in mammals, has been a subject of scientific speculation for a long time. It has been shown that in many vertebrate and invertebrate species, the sex of an individual is determined by the individual's chromosomal constitution. Initial studies of classical genetic searching for sex-transforming mutations and the scrupulous analyses of modified phenotypes have shed light on the mechanism(s) of sex-determination. They paved the road to successful studies at molecular level. After a brief review on sex determination in chosen model species, the “Drosophila system” is presented to exemplify a possible general principle for sex determinism.     

Ejaculate size varies with socio-sexual situation in an insect

Abstract.

• 1 Males operate within a finite energy budget and cannot produce limitless supplies of sperm. On the other hand, when a female mates with a second male while still containing fertile sperm from a rival male, selection should favour the male that inseminates more sperm. Optimal strategy should thus be for males to exercise discretion in the allocation of sperm to individual females. Assuming the outcome of sperm competition to be based on either the raffle or kamikaze principles, the sperm competition hypothesis predicts a positive association between the probability that the sperm will find themselves in competition with sperm from rival males and the number of sperm inseminated.
• 2 The beetle, Tenebrio molitor L., behaves in accordance with this hypothesis. Males accompanied by a rival male before and during mating inseminate more sperm per ejaculate than unaccompanied males. Accompanied males are also faster to initiate mating and more likely to show post-copulatory guarding. Adjustment of number of sperm inseminated was shown by males subjected to both long-term (5 days) and short-term (5 min) exposure to potential intrasexual competitors. Individual males exposed to both levels also demonstrated the ability to adjust their ejaculate according to socio-sexual situation.
• 3 We conclude that male T.molitor adjust the number of sperm they inseminate according to some perception of the risk of sperm competition.

     

Morphology and life cycle of Ceratium rhomvoides nov. sp. (Dinophyceae) from the lake Plußsee (Federal Republic)

A new species of freshwater dinoflagellates, Ceratium rhomvoides nov. sp., is described from the Plußsee, northern West Germany, where it occurs regularly. C. rhomvoides nov. sp. is distinguished from closely related taxa by various aspects of the morphology of the vegetative cell and the cyst and by its sexual reproduction and seasonal distribution.     

Sexual reproduction and life cycle of Ceratium furcoides (Dinophyceae) in situ in the lake Plußsee (F.R.)

The life cycle of Ceratium furcoides (Levander) Langhans which features sexual reproduction is described for the first time in situ from the lake Plußsee (northern West Germany). Anisogamic copulation occurs during the bloom period in July–August by incorporation of the male gamete by the female gamete, resulting in an overwintering planozygote. The planozygote develops into a benthic hypnozygote which germinates in spring to establish a planomeiocyte. The morphology and structure of the stages of the life cycle are described using light and scanning electron microscopy.