Variation in pelvic size between males and females

Selection intensity and phenotypic variability are inversely related. It has been hypothesized that, owing to opposing selection pressures on pelvic morphology in females between efficiency in locomotion and obstetric adequacy, female pelvic morphology is less variable than that in males. The hypothesis was supported based on data derived from observational methods of sexing pelves (Meindl et al., 1985). The hypothesis was tested in the present study based on a metrical analysis of the true pelvis. The results show that there are no sexual differences in pelvic variability. Consequently, while males and females are equally variable in the dimensions of the true pelvis, the visual cues that osteologists use to sex pelves are more variable in males.     

Differences in rat kidney morphology between males, females and testosterone-treated females.

Kidneys of normal female and male Wistar-Kyoto rats were studied by standard morphological techniques and morphometry in order to evaluate possible differences in the overall kidney morphology between both sexes. Furthermore, we investigated the role of testosterone (DHT) on kidney morphology by treating females with daily DHT injections. Kidney weight and volume in relation to body weight were not significantly different between males and females and were not affected by DHT. Differences were found in the volume distribution among the kidney zones. The cortex was larger in males than in females, whereas the medulla was conspicuously larger in females than in males. The greater volume of the cortex in males was mainly due to a more extensive development of proximal tubules. DHT treatment in females increased the volume of their proximal tubules. Glomerular volume was similar among the three groups. Within the medulla, the difference was most prominent in the inner stripe (14.9% of the total kidney volume in females vs. 8.9% in males) and was also important in the inner medulla (7.0 vs. 4.8%). The absolute epithelial volume of thick ascending limbs in this zone was larger in females than in males. This difference was more pronounced in short loops (approximately 20%) than in long loops (approximately 10%). The values of the DHT-treated females ranged in between. In spite of the greater development of medulla and thick ascending limbs in females, urine concentration was higher in males than in females and maximum urinary concentrating ability after 48 h dehydration was not different between both sexes.     

Differences in feeding activity between females and males of Temora longicornis

We have studied experimentally in the laboratory the behavioural responses of females and males of the calanoid copepodTemora longicornis and their encounter probability with the alga Rhodomonas. Both sexes of this calanoid copepod adapted their motion velocity and style of swimming in reaction to the presence of prey. Their mean velocity, as well as the probability of high velocity values, increased in the presence of the algae. Moreover, the time spent in swimming activity increased, reflecting a possible adaptation in order to facilitate encounter with prey. Females were more sensitive to the presence of food: mean velocities showed a 40 % increase for males, from control to food conditions, whereas for females the increase was 240 %. This result was confirmed using several indicators: net-to-gross displacement ratio, probability density functions, and symbolic dynamics. This may indicate that female T. longicornis are more attracted by food than males.     

Genetic conflicts of interest in plants

Several features of the reproductive biology of seed plants have recently been explained using kin-selection interpretations. The simultaneous presence of tissues with different genetic make-ups during several phases of a seed-plant's life cycle is a feature that sets the conditions for agonistic interactions among selfish genes. The available empirical evidence indicates that genetic conflicts of interest are prevalent phenomena in seed plants. Recent research on the patterns of endosperm gene transmission provides a framework for new interpretations of the role of inclusive fitness in plants.     

Discrimination between males and females by scent in Lemur fulvus.

Two captive male Lemur fulvus were presented with scents of conspecific males and females, outside the mating season. Both subjects sniffed male scents significantly more than female scents. Male and female scents did not elicit significantly different amounts of scent marking. None of the responses of either subject suggested any discrimination of sub-species by scent.     

Differences in response to defoliation between males and females of Silene dioica

Summary The response by male and female plants to herbivory was studied by experimental defoliation of the dioecious perennial herb Silene dioica in a green-house. Male and female plants were defoliated prior to and during the early flowering phase at two intensities (50% and 100% of leaf-area removed) in two consecutive years. Defoliation resulted in a decrease in the number of flowers initiated in both sexes, while a larger delay of peak flowering and a higher mortality was observed in males compared to females. In female plants, severe defoliation resulted in a reduction in seed number per capsule and in seed size compared to control. Females showed a negative correlation between the production of flowers in the first and second season in all treatments, while flowering in males the first season was not correlated with flowering in the second season. Females also showed a lower frequency of flowering than males during the two seasons studied. However, during the flowering period, males allocated significantly more biomass to flowers than did females. This outcome supports the idea that females may have a higher total reproductive expenditure than males, but males have a higher reproductive effort during flowering. Male rosette leaves were significantly preferred by the generalist herbivore Arianta arbustorum in experiments. This preference was most pronounced in trials with leaves from fertilized plants compared to nonfertilized plants. A greater storage of resources in aboveground leaves during winter by males compared to females may explain the higher preference for male leaves and the higher male mortality following early defoliation. Furthermore, males are smaller than females and may have a lower ability than females to replace lost resources needed for reproduction when defoliated early in the season.     

Migration load in males and females

Many theories have been proposed for interpreting the relative sexual mortalities in natural populations, but the effects of maladaptive genes from migrants on sexual mortality have not been examined. In this study, I systematically explore the properties of migration load in dioecious plants where gender dimorphism is determined by sex chromosomes (the XX-XY or similar system). Two stages of gene flow (pollen and seed) and two stages of selection (gametophyte and sporophyte) are jointly examined in the one- and two-locus cases. The general results show that several factors, including the maladaptive allele frequencies in migrants, migration rate, selection, and linkage disequilibria, can individually or jointly alter the relative sexual mortalities at either the gametophyte or the sporophyte stage, or both. When there are the same values between sexes in the parameters relevant to the migrant gene frequencies and two-stage selection coefficients under the additive viability model (without Y-chromosome and linkage disequilibrium effects), the average mortality is higher in ovules than in pollen since the males do not inherit the maladaptive genes from migrating pollen. The average mortality per individual in the homogametic sex is almost twice as large as that in heterogametic sex at the sporophyte stage. Under the additive viability model, the relative sexual mortalities at the gametophyte stage are negatively related to the relative sexual mortalities at the sporophyte stage.     

Larger swordtail females prefer asymmetrical males

Many organisms, including humans, find symmetry more attractive than asymmetry. Is this bias towards symmetry simply a by-product of their detection system? We examined female preference for symmetry of the pigment pattern vertical bars in the swordtail fishes Xiphophorus cortezi and Xiphophorus malinche. We found a relationship between preference for symmetry and female size, with larger and thus older females spending significantly more time with the asymmetrical video animation as compared to the symmetrical video animation. The preference for asymmetry we report demonstrates that even if females can detect symmetrical males better, this does not preclude subsequent selection on females to prefer symmetrical or asymmetrical males. In addition, because the preference was correlated with female size, past studies may have missed preference for either asymmetry and/or symmetry by not examining the relationship between female preference and size/age or by measuring a limited size/age distribution of females. In both of the species of swordtail fishes examined, a high proportion of males are asymmetrical by more than one bar. We suggest that female preference may be maintaining fluctuating asymmetries in these fishes.     

Evolutionary conflicts: rapid suppression of a male-killer

Conflicts between and within species can drive fast evolutionary change. A recent study has documented remarkably rapid counter-adaptations in the wild to an extreme sex-ratio distortion caused by a bacterial symbiont.     

Trade-offs, conflicts of interest and manipulation in Plasmodium-mosquito interactions

A long-held view among parasitologists is that infection by malaria parasites does not harm the mosquito vector. One of the reasons for this belief is that the two partners of the association share interests in the most important life-history traits of the mosquito. Both partners benefit from increased survival and an increased rate of bloodfeeding the mosquito to increase its reproductive success and the parasite to ensure its transmission. Problems with this line of reasoning appear when one considers possible trade-offs among the mosquito's life-history parameters, which constrain the attempts by the mosquito and the parasite to maximize their success. Could these constraints differ between the two partners and thus lead to conflicts of interest and what would be the evolutionary and epidemiological consequences of conflicting interests? These questions will be investigated below.