Effects of prepubertal castration on the spinal motor nucleus of the ischiocavernosus muscle of the rat

Summary The location, number and size of the motoneurons innervating the ischiocavernosus muscle, identified by means of horseradish-peroxidase (HRP) retrograde transport, were studied (1) in adult untreated male rats, (2) in adult male rats castrated before puberty, and (3) in adult male rats castrated before puberty and injected with testosterone from the day of castration. After injection of HRP into the ischiocavernosus muscle, labeled motoneurons were found in the dorsolateral and dorsomedial columns of the lamina IX, at the level of L6 and S1 segments of the spinal cord. Morphometric analysis demonstrated that prepubertal castration induces a statistically significant reduction in the somatic and nuclear areas (40% and 35%, respectively, if compared to those of the control rats) of both the dorsolateral and dorsomedial motoneurons, but does not affect their number. The effects of castration are prevented by exogenous testosterone.Preliminary results were presented at the International Conference on Hormones, Brain and Behaviour, Liège, Belgium, August, 1989     

Sexual size dimorphism and selection in the wild in the waterstrider Aquarius remigis: Body size,components of body size and male mating success

Sexual size dimorphism is assumed to be adaptive and is expected to evolve in response to a difference in the net selection pressures on the sexes. Although a demonstration of sexual selection is neither necessary nor sufficient to explain the evolution of sexual size dimorphism, sexual selection is generally assumed to be a major evolutionary force. If contemporary sexual selection is important in the evolution and maintenance of sexual size dimorphism then we expect to see concordance between patterns of sexual selection and patterns of sexual dimorphism. We examined sexual selection in the wild, acting on male body size, and components of body size, in the waterstrider Aquarius remigis, as part of a long term study examining net selection pressures on the two sexes in this species. Selection was estimated on both a daily and annual basis. Since our measure of fitness (mating success) was behavioral, we estimated reliabilities to determine if males perform consistently. Reliabilities were measured as ? statistics and range from fair to perfect agreement with substantial agreement overall. We found significant univariate sexual selection favoring larger total length in the first year of our study but not in the second. Multivariate analysis of components of body size revealed that sexual selection for larger males was not acting directly on total length but on genital length. Sexual selection for larger male body size was opposed by direct selection favoring smaller midfemoral lengths. While males of this species are smaller than females, they have longer genital segments and wider forefemora. Patterns of contemporary sexual selection and sexual size dimorphism agree only for genital length. For total length, and all other components of body size examined, contemporary sexual selection was either nonsignificant or opposed the pattern of size dimporhism. Thus, while the net pressures of contemporary selection for the species may still act to maintain sexual size dimorphism, sexual selection alone does not.     

Intraspecific variation of Eolophiodon laboriense,a basal Lophiodontidae (Mammalia,Perissodactyla) from the early Eocene of Southern France

The Lophiodontidae is an emblematic and well-documented Eocene family of perissodactyls from Western Europe. However, after more than a century and a half of studies, lophiodontids still display a complex systematics associated with blurry intraspecific variation and a poorly known early radiation. The locality of La Borie, located near the city of Toulouse, France, has yielded numerous remains of Eolophiodon laboriense. This abundance of remains allows for the first time the study of the intraspecific variation of a basal lophiodontid. The variation has been investigated for dental and cranio-mandibular characters, notably dental polymorphism, size variation and sexual dimorphism. The intraspecific variation of E. laboriense is high with more than 20 polymorphic characters of the dentition, including many additional crests and conules. This dental polymorphism is similar to the one observed in the Bartonian lophiodontid Lophiodon lautricense. E. laboriense also displays an important degree of sexual dimorphism, with male specimens having broader and longer mandibles with larger canines than females. Despite this high intraspecific variation, the low size variation of teeth and the consistency of diagnostic characters strengthen the validity of the genus Eolophiodon and does not impact the previous lophiodontid phylogeny.     

The occurrence and frequency of 2n pollen in 2x, 4x,and 6x wild,tuber-bearing Solanum species from Mexico,and Central and South America

Summary The occurrence of 2n pollen-producing plants was investigated in 187 plant introductions (PIs) of 38 wild species of tuber-bearing Solanum. These 2x, 4x, and 6x species are from Mexico, and Central and South America. The determination of 2n pollen-producing plants was conducted using acetocarmine glycerol. Plants with more than 1% large-size pollen were regarded as 2n pollen-producing plants. 2n pollen-producing plants were identified in the following species: 10 out of 12 Mexican 2x species, seven of nine South American 2x species, seven of seven Mexican and Central American 4x species, five of five South American 4x species, and five of five Mexican 6x species. The frequency of 2n pollen-producing plants varied among species at the same ploidy level, but the range of frequency, generally between 2 and 10% among species, was similar over different ploidy levels. The general occurrence of 2n pollen in both 2x and polyploid species, which are evolutionarily related, is evidence that the mode of polyploidization in tuber-bearing Solanums is sexual polyploidization. Furthermore, the frequencies of 2n pollen-producing plants in autogamous disomic polyploid species were not markably different from those of their related diploid species. It is thought that the frequent occurrence of 2n gametes with autogamy tends to disturb the fertility and consequently reduce fitness of polyploids. Thus, we propose that the breeding behavior of polyploids and the occurrence of 2n gametes may be genetically balanced in order to conserve high fitness in polyploid species in tuberbearing Solanum.Paper No. 3114 from the Laboratory of Genetics. Research supported by the College of Agriculture and Life Sciences; International Potato Center; USDA, SEA, CGRO 84-CRCR-1-1389; and Frito Lay, Inc.     

Sexual dimorphism in the growth of the cranium

The major sexual dimorphisms in body size appear at puberty but, by then, 95% of the growth of the cranium is completed. As sexual dimorphism in the cranium is as great as for other parts of the body, this suggests that it must appear at an earlier age, and that cranium/body size ratios for the two sexes will vary during growth. Results from a longitudinal study of Montreal children are used to investigate this phenomenon. The effect is expressed quantitatively by proportional growth and growth velocity curves, based on the final size of boys, which show that the dimorphism indeed makes an early appearance. The data are also analyzed on an age scale relative to the ages of peak growth velocity in stature, derived from the individual growth curves. This shows that although there is a minor pubertal spurt in growth for the external cranial dimensions of boys, it contributes relatively little to the final dimorphism in cranial size. To summarize this aspect of growth, an index of cephalization is calculated: head length × head width/stature. Cross-sectional standards for the change of the mean index with age show a linear decline for boys and girls until puberty, with a constant difference between them. After puberty, the index becomes equal in the two sexes. Individual development curves for the index are however not linear.     

Nucleotide pool changes in coelomic cells (eleocytes) of the polychaete Nereis virens during sexual maturation

Eleocytes (a type of coelomic cell) of the polychaete Nereis virens can store large amounts of adenine nucleotides at certain times. Since eleocytes have specific functions related to gametogenesis, we tested whether the presence of these large nucleotide stores in eleocytes is specific to gender or related to specific events during gametogenesis. Nucleotide pools in eleocytes isolated at different stages of sexual maturation from N. virens were analysed using high-performance liquid chromatography. Eleocytes from immature and male animals had extremely high concentrations of both AMP and ADP (each > 10 μmol/ml of packed cell volume). In eleocytes from male animals, the high nucleotide stores were maintained throughout the maturation phase and decreased at a late stage, while in female animals the nucleotides were degraded at an early stage of maturation. In male eleocytes, the decrease in the adenine nucleotide pool may be the result of its conversion to inosine which is then released by the eleocytes and reutilized by male germ cells for nucleic acid biosynthesis, as has been suggested previously. Our study shows that the time of degradation of the adenine nucleotide pool coincides with the period of spermatogonia proliferation which involves intense nucleic acid synthesis. ATP levels (0.4–1.5 μmol/ml packed cell volume) and the guanine nucleotide pool (GTP+GDP+GMP; 0.08–0.18 μmol/ml packed cell volume) were similar in both sexes, did not change during germ cell development and were decreased only in eleocytes from prespawning females. The GTP/GDP ratios were initially higher (up to 14) in eleocytes from females compared to ratios in eleocytes from immature (4–9) and male animals (up to 8), and decreased during the maturation phase of the animals. GTP levels were correlated with those of ATP; this correlation was much closer in eleocytes from females than from males. The results further support the hypothesis that the adenine nucleotide stores in the eleocytes are maintained as a supply of purine precursors for the growing germ cells.     

Univariate and multivariate methods for sexing the sacrum

Metric data on 200 sacra of known sex, age and race are analyzed to determine the usefulness of conventional observations for determining sex in this bone. Results of the univariate analysis show that significant sex differences in the sacrum involve primarily the top portion of the bone for both whites and blacks. However, measurements of curvature are important sex differences in the sample of blacks. A new index relating the S1 body to sacral breadth is proposed as more useful in classifying the bones by sex than indices involving other measurements. Discriminant analysis shows that the sample of whites can be analyzed significantly better by this method than by using an index. The choice of univariate or multivariate method must depend on the condition of the bone, and will be influenced to some extent by the race from which the sample is drawn.     

Population dynamics ofGlaux maritima (L.) along a distributional cline

Population fluctuations ofGlaux maritima, along a transect on a Baltle sea shore meadow, were recorded between 1979 and 1983. A bimodal distribution in numbers along the transect reflects the variation in factors regulating numbers: The two maintenance systems of the species, vegetative propagation and sexual reproduction play different roles. Vegetative propagation is fast and responds quickly to variations in the environment. The seeds germinate in strongly fluctuating temperatures which are triggered by disturbances such as flooding, damaging the vegetation.     

Risk of sperm competition does not influence copulatory behavior in the promiscuous meadow vole (<Emphasis Type="Italic">Microtus pennsylvanicus</Emphasis>)

It is not clear whether males in all mammalian species adjust their copulatory behavior when faced with risk of sperm competition (RSC). Previous work on meadow voles, Microtus pennsylvanicus, indicated that males increase their sperm expenditure but not the number of ejaculations in the presence of odors of a conspecific male. The present study follows up on this work and asks whether male meadow voles modify any aspect of their copulatory behavior when they face a RSC. We examined 46 variables of copulatory behavior and found that the presence of odors from a conspecific male did not affect any of these variables. Thus, male meadow voles, unlike some other species of mammals, do not adjust their copulatory behavior when exposed to cues associated with an elevated RSC.     

Mate choice in modern societies

Most research on mate choice in modern societies is based on data that may or may not reflect actual mating behavior (e.g., stated preferences, personal advertisements). In the present study, real-life matings were reported by a large representative sample of men and women (N = 1,133). These data were used to test an evolutionary model in which mate choice is hypothesized to depend on resources potentially contributed to reproduction by each sex. Consistent with the model, it was found that (a) men (but not women) of higher social status acquire more mating partners, suggesting that male status is an important criterion in female choice; (b) women’s (but not men’s) number of partners decreases linearly with age, suggesting that female reproductive potential is an important criterion in male choice; and (c) women (but not men) display a significant relationship between marital dissolution and promiscuity, suggesting that female sexual exclusivity is an important criterion in male choice. These results are discussed in relation to understanding mate choice mechanisms from behavioral data. Daniel Pérusse is an assistant professor in the Department of Anthropology at the Université de Montréal. His research interests include the evolutionary biology of human social and reproductive behavior, sexual selection theory, and biocultural evolution. His current research bears on human socialization processes and psychosocial development from an evolutionary and behavior-genetic perspective. Recent publications include “Cultural and Reproductive Success in Industrial Societies: Testing the Relationship at the Proximate and Ultimate Levels” (Behavioral and Brain Sciences 16(2):267–322, 1993) and “Human Parental Behavior: Evidence for Genetic Influence and Potential Implications for Gene-Culture Theory” with M. C. Neale, A. Heath, and L. J. Eaves (Behavior Genetics, in press).