Sexual differences in larval life history traits of acanthocephalan cystacanths

Sexual differences in life history traits, such as size dimorphism, presumably arise via sexual selection and are most readily observed in adults. For complex life-cycle parasites, however, sexual selection may also have consequences for larval traits, e.g., growth in intermediate hosts. Two acanthocephalan species (Acanthocephalus lucii and Echinorhynchus borealis) were studied to determine, whether larval life histories differ between males and females. The size of female A. lucii cystacanths had a much stronger relationship with intermediate host size than males, suggesting females invest more in growth and are consequently more limited by resources. No relationship between host size and cystacanth size was observed for E. borealis. For both species, female cystacanths survived longer in a culture medium composed entirely of salts, which could suggest that females have greater energy reserves than males. A comparative analysis across acanthocephalan species indicated that sexual size dimorphism at the adult stage correlates with cystacanth dimorphism. However, the relationship was not isometric; cystacanths do not reach the same level of sexual dimorphism as adults, possibly due to resource constraints. Our results suggest that larval life histories diverge between males and females in some acanthocephalans, and this is seemingly a consequence of sexual selection acting on adults.     

Morphological versus acoustic analysis: what is the most efficient method for sexing yelkouan shearwaters Puffinus yelkouan?

Sexing monomorphic seabirds is particularly difficult, and available methods have various disadvantages, such as seasonal non-applicability or stress induction. The yelkouan shearwater Puffinus yelkouan is a poorly studied seabird endemic to the Mediterranean basin. Ecological and biological data are needed for this species, thus necessitating the development of appropriate field methods. Here, we tested two methods for sexing yelkouan shearwaters: the classical morphological method and a new acoustic method. Morphological analysis demonstrated sexual differences in head, leg and feather measurements, with a high degree of overlap resulting in only 87.2% accuracy. In contrast, acoustic analysis showed that the highest value of the fundamental frequency (FC) and duration of the clear note of calls did not overlap between males and females. Yelkouan shearwaters can be sexed with 100% accuracy by measuring FC. If FC < 678.4 Hz, the bird is female, while if FC > 678.4 Hz, the bird is male. Other advantages of this method are its simplicity and non-invasiveness, which are particularly important for a potentially threatened species.     

Habitat use and mating system of the houbara bustard (Chlamydotis undulata undulata) in a semi-desertic area of North Africa: implications for conservation

Studies of the movements and home-ranges of houbara bustards (Chlamydotis undulata undulata) showed sexual and seasonal differences in the use of space, with a polygynous mating system similar to an ‘exploded-lek’ or a ‘resource-defence-polygyny’, that remains undefined. We used the arthropod biomass as an index of the trophic quality of six defined habitats and we radio-tracked 7 females and 13 males to test whether sexual and seasonal variations in habitat use were related to resource availability, and to verify if critical resources for breeding females were monopolised by males. We analysed habitat selection in both sexes separately. We used the habitat type composition of buffer zones around radio-locations to study annual and seasonal habitat selection and to identify preferred habitats, using the chi-square goodness-of-fit test. Habitat use between sexes and between seasons were compared using MANOVA based on log-ratios of habitat proportions. During the year, and in each season, both sexes appeared to be significantly selective for habitats in comparison to their availability. But males avoided esparto grass, while females used all habitats. Habitat use differed between sexes in the breeding season, but not in the non-breeding season. In spring, when food resources were abundant and uniformly distributed in space, males preferred ‘temporarily flooded areas’ and females preferred ‘reg with tall perennials’ that offered both food and cover for brooding. Critical resources were not monopolised by males and the mating system fulfilled the definition of the ‘exploded-lek’. Leks are key sites for reproduction and should be considered as priority areas in further conservation plans.     

Sexual behavior of male pigs

Two major characteristics of males that affect the likelihood of achieving copulation are the sexual motivation and mating competency of the male. The behavior of domestic animals, including their sexual behavior, is dependent upon a complex interaction between the organism's internal and external environment. In male pigs, as in other mammalian species, it is clear that testicular steroids are required to maintain sexual behavior and testosterone plays a critical role. Consistent with studies in other species, it is apparent in male pigs that there is a threshold circulating concentration of androgens and/or estrogens required to maintain sexual behavior and that the level of sexual motivation is unrelated to levels of sex steroids providing these are adequate for normal sexual behavior. Key aspects of the external environment that affect the sexual behavior of the male pig include genetic, seasonal, social, sexual and psychological factors.     

Effect of culture density and volume on <Emphasis Type="Italic">Moina micrura</Emphasis> (Kurz, 1874) reproduction,and sex ratio in the progeny

Moina micrura is a cosmopolitan, cyclic parthenogenetic, cladoceran with ample morphological and ecological plasticity that inhabits temperate, tropical, and subtropical regions of the world. Sexual reproduction in cladocerans is a phenomenon induced by environmental factors, mainly associated with adverse conditions, including crowding. In this study we have assessed the effects of population density combined with the volume available for individual development, on the number of newborns and on the sex ratio in the progeny. Three parthenogenetic female densities (D ₁ = 33 ind l⁻¹, D ₂ = 66 ind l⁻¹, D ₃ = 100 ind l⁻¹) were assayed in combination with three culture volumes (V ₁ = 30 ml, V ₂ = 60 ml, V ₃ = 120 ml), at 21°C. Once the reproduction began, progeny was isolated daily and counted, identifying female and male neonates. Culture volume was the only factor that had a significant effect on the total progeny, as well as on the number of males in the progeny; the highest sex ratio was recorded in D ₂ V ₁ (0.58), whereas the lowest was for D ₁ V ₃ (0.06). Female density had no significant effect on the number of sexual M. micrura. We hypothesize that male production (quantity and frequency) was higher in the lowest tested volume because of a reduction in the space available per individual, but not necessarily associated with the physical interaction related with a high encounter rate in more crowded conditions. Guest editor: Piet Spaak Cladocera: Proceedings of the 7th International Symposium on Cladocera     

Relationship between testosterone and interest in sexual stimuli: the effect of experience

Testosterone is commonly thought to drive male sexual interest, but little experimental evidence demonstrates a direct relationship between natural variation in testosterone and sexual interest in healthy young men. This study measured young men's testosterone levels and their interest in visual sexual stimuli across three test sessions within 1 month. Fifteen men aged 23–28 viewed pictures of couples engaged in sexually explicit activity. Each session included a unique set of 72 pictures depicting heterosexual oral sex or intercourse presented in randomized order. Participants controlled how long they viewed each picture, with viewing time indicating sexual interest. Men's testosterone (T) levels were assayed from blood spots obtained prior to viewing the pictures. Overall, T and viewing time were positively correlated; however, the strength of this relationship varied by test session. T was marginally correlated with viewing time during the first session (r = 0.43) and not significantly correlated with viewing time on the second session (r = 0.16). During the final test session, when habituation might influence male interest in the stimuli, T was strongly correlated with viewing time (r = 0.80). Thus, the current study demonstrates a direct but context dependent relationship between testosterone and sexual interest in healthy young males.     

The orang-utan mating system and the unflanged male: A product of increased food stress during the late Miocene and Pliocene?

The orang-utan is unique among apes in having an unusually long male developmental period and two distinct adult male morphs (flanged and unflanged), which generally, but not exclusively, employ different reproductive strategies (call-and-wait vs. sneak-and-rape). Both morphs have recently been shown to have roughly similar levels of reproductive success in the one site where such a study has been conducted. This is in stark contrast to the unimale polygynous gorilla, in which dominant males sire almost all infants. Despite this, evidence on sexual dimorphism, life history, diet, and socioecology of extant and extinct apes, as well as the ontogeny, reproductive morphology, and physiology of extant apes, all indicate that the orang-utan's present-day mating system most likely evolved from a gorilla-like base, with one dominant male guarding a harem of females. The available evidence indicates that, due chiefly to the likely onset of the El Ni?o Southern Oscillation (generally regarded as the trigger for mast fruiting in dipterocarps) approximately 3-5Ma, southeast Asian forests would have begun to experience longer and more severe periods of low food availability. This change in food availability would have meant that full-time gregariousness was no longer energetically tolerable and, as a result, females dispersed more widely in search of food and adult/flanged males were no longer able to effectively guard a harem of females. A niche for a quiet, quick, opportunistic "sexual predator" (i.e., the unflanged male) then became available. This finding implies that, despite being anatomically quite chimpanzee-like, the ancestral hominoid probably had a social and mating system more similar to the gorilla than any other living ape.     

Transgenic cassava resistance to <Emphasis Type="Italic">African cassava mosaic virus</Emphasis> is enhanced by viral DNA-A bidirectional promoter-derived siRNAs

Expression of double-stranded RNA (dsRNA) homologous to virus sequences can effectively interfere with RNA virus infection in plant cells by triggering RNA silencing. Here we applied this approach against a DNA virus, African cassava mosaic virus (ACMV), in its natural host cassava. Transgenic cassava plants were developed to express small interfering RNAs (siRNA) from a CaMV 35S promoter-controlled, intron-containing dsRNA cognate to the common region-containing bidirectional promoter of ACMV DNA-A. In two of three independent transgenic lines, accelerated plant recovery from ACMV-NOg infection was observed, which correlates with the presence of transgene-derived siRNAs 21–24 nt in length. Overall, cassava mosaic disease symptoms were dramatically attenuated in these two lines and less viral DNA accumulation was detected in their leaves than in those of wild-type plants. In a transient replication assay using leaf disks from the two transgenic lines, strongly reduced accumulation of viral single-stranded DNA was observed. Our study suggests that a natural RNA silencing mechanism targeting DNA viruses through production of virus-derived siRNAs is turned on earlier and more efficiently in transgenic plants expressing dsRNA cognate to the viral promoter and common region.     

Transgenic <Emphasis Type="Italic">Nicotiana benthamiana</Emphasis> plants resistant to cucumber green mottle mosaic virus based on RNA silencing

RNA silencing technology was used to confer resistance to cucumber green mottle mosaic virus (CGMMV). Nicotiana benthamiana was transformed with a transgene designed to produce an inverted repeat RNA containing CGMMV-coat protein gene (CP) sequences, which were separated by an intron sequence, under the control of the cauliflower mosaic virus 35S promoter. We attempted to confirm the resistance of seven independent transgenic lines; five lines showed resistance to CGMMV infection. The systemic spread of virus was prevented after the inoculation of CGMMV, and the CP-specific short interfering RNA (siRNA) was detected in resistant lines. Thus, the resistance against CGMMV through RNA silencing is strong and efficient.     

The influence of conspecific chemical cues on walking behavior of <Emphasis Type="Italic">Ixodes ricinus</Emphasis> males

The influence of female and male cues on the male searching behavior of the sheep tick, Ixodes ricinus (Acari: Ixodidae), was studied under constant laboratory conditions by means of a computerized video tracking system. Males were released into an open glass arena in which one half had been exposed for 1 h to 5 freely walking unfed females or five males. The obtained track data were analyzed to reveal if male walking pattern was random or affected by cues of conspecifics left on the arena surface. The results showed that males spent significantly more time and walked a significantly longer distance in the area with female cues compared to the control area. Moreover, the walking path of males was more tortuous on the cues half than the control half. In contrast, walking behavior of males was not affected by male cues in any observed parameter. These results provide the first evidence that unfed females leave sex-specific semiochemicals on a substrate during their walk and that these cues have an effect on male searching behavior. Since this effect was not observed when female cues were 24-h old, the semiochemicals seem to either evaporate or are subject to degradation. The biological significance of these findings for mate-searching in I. ricinus males is discussed.