PHYLOGENETIC RELATIONSHIPS WITHIN THE COLONIAL VOLVOCALES (CHLOROPHYTA) INFERRED FROM CLADISTIC ANALYSIS BASED ON MORPHOLOGICAL DATA1

A cladistic analysis was used to deduce the phylogenetic relationships within the colonial Volvocales. Forty-one pairs of characters related to gross morphology and ultrastructure of vegetative colonies as well as asexual and sexual reproduction were analyzed based on parsimony, using the PAUP 3.0 computer program, for 25 species belonging to nine volvocacean and goniacean genera of the colonial Volvocales. Chlamydomonas reinhardtii Dangeard was the outgroup. The strict consensus tree indicated the presence of two monophyletic groups, one composed of all the volvocacean species analyzed in this study and the other containing the goniacean species except for the four-celled species Gonium sociale (Dujardin) Warming. In addition, these two groups constitute a large monophyletic group, to which G. sociale is a sister group. A new combination Tetrabaena socialis (Dujardin) Nozaki et Itoh and a new family Tetrabaenaceae Nozaki et Itoh are thus proposed for G. sociale. In addition, the analysis suggests that the volvocacean genera Eudorina and Pleodorina are paraphyletic groups, respectively, and that the monotypic genus Yamagishiella has no autapomorphic characters and represents primitive features of the anisogamous and oogamous genera of the Volvocaceae. Phylogenetic relationships within the Volvocaceae and the Goniaceae, as well as the various modes of sexual reproduction exhibited by these organisms, are discussed on the basis of the analysis.     

Flash behavior of femalePhoturis versicolor fireflies (Coleoptera: Lampyridae) in simulated courtship and predatory dialogues

FemalePhoturis versicolor fireflies attempt to capture males by responding to heterospecific flash patterns. A mating-dependent switch occurs which affects response timing and frequency of female flashes. We examined the switch using females of known age, mating status, and flash experience to assess how accurate mimicry is, what factors influence it, and what mechanism produces it. Presentations of simulated male flash patterns before and after mating revealed elements of an entrainment mechanism controlling female responsiveness. Unmated females preferentially answered conspecific patterns with variable latencies, averaging 1 s. Mating induced changes in both response frequency and response latency: Females answered heterospecific patterns more frequently, and latencies elicited by conspecific patterns shifted away from the unmated range. Heterogeneity in mean and variance of response latency among individuals indicates that females do not share a discrete reply to a given pattern. Little correspondence exists between latencies of sympatric species andP. versicolor females, suggesting that the flash response mechanism produces entriainment to any rhythmic pattern, not a one-to-one matching between prey and predator latencies. Different selective scenarios underlie strict mimicry versus entrainment mimicry.     

Pathogenesis of SIVmac251 after atraumatic inoculation of the rectal mucosa in rhesus monkeys

Intrarectal inoculation of rhesus monkeys with low doses of SIV_mac led to a prolonged clinical and virological latency that was not observed for high intrarectal doses or for intravenous inoculation. Animals infected intrarectally with low virus doses remained negative for serum antibody responses to SIV for at least one year even though they readily transferred SIV to naive recipients via transfusion of whole blood.     

Selection of buffalo bulls: Sexual behavior and its relationship to semen production and fertility

Forty-four buffalo bulls, used for artificial insemination, were studied to develop libido, mating ability and sexual behavior indices for selection purposes. For each index, 5 categories (i.e., excellent, very good, good, fair and poor) were established. The sexual behavior index was found to be more reliable than the libido and mating ability indices. Buffalo bulls in good to excellent categories were considered acceptable sires.

Reaction time, sexual aggressiveness, and scores of libido, mating ability and sexual behavior differed significantly among the various categories of the 3 indices. Libido significantly correlated with mating ability (r=0.89; P<0.001). Sexual behavior expressed significant relationship with age (r=0.41; P<0.01) and body weight (r=0.48; P<0.01), but was nonsignificant with the scrotal circumference (r=0.28; P>0.05) of buffalo bulls. However, these relationships were absent (P>0.05) in the acceptable sires. Semen production was correlated with sexual behavior in only the fair and poor categories of buffalo bulls (r=0.84; P<0.005). Sexual behavior had no relationship with the fertility rate of buffalo bulls (r=0.44; P>0.05). It is concluded that the sexual behavior index can be used successfully for the selection of buffalo bulls. Excellent- to good bulls should be used in an artificial breeding program if they qualify in the other selection indices.     

Temperature-dependent sex determination in reptiles: Proximate mechanisms,ultimate outcomes,and practical applications

In many egg-laying reptiles, the incubation temperature of the egg determines the sex of the offspring, a process known as temperature-dependent sex determination (TSD). In TSD sex determination is an “all or none” process and intersexes are rarely formed. How is the external signal of temperature transduced into a genetic signal that determines gonadal sex and channels sexual development? Studies with the red-eared slider turtle have focused on the physiological, biochemical, and molecular cascades initiated by the temperature signal. Both male and female development are active processes—rather than the crganized/default system characteristic of vertebrates with genotypic sex determination—that require simultaneous activation and suppression of testis- and ovary-determining cascades for normal sex determination. It appears that temperature accomplishes this end by acting on genes encoaing for steroidogenic enzymes and steroid hormone receptors and modifying the endocrine microenvironment in the embryo. The temperature experienced in development also has long-term functional outcomes in addition to sex determination. Research with the leopard gecko indicates that incubation temperature as well as steroid hormones serve as organizers in shaping the adult phenotype, with temperature modulating sex hormone action in sexual differentiation. Finally, practical applications of this research have emerged for the conservation and restoration of endangered egg-laying reptiles as well as the embryonic development of reptiles as biomarkers to monitor the estrogenic effects of common environmental contaminants. © 1994 Wiley-Liss, Inc.     

Sexual differentiation of brain and behavior in the zebra finch: Critical periods for effects of early estrogen treatment

In order to determine the critical period(s) during which estrogen alters sexually dimorphic behavior and neuroanatomy in zebra finches (Poephila guttata), nestlings were injected daily 20 μg estradiol benzoate (EB) during posthatching week 1, week 2, week 3, or weeks 1, 2, and 3. At 7 months of age, birds were implanted with testosterone propionate and tested with female partners for singing, dancing, and copulatory mounting. Brains were subsequently processed for morphometry, and the volumes of the song system nuclei HVC, area X, and RA and the soma sizes and densities of neurons in RA were determined. Males given EB during week 1 failed to mount. Females given EB during week 1 were fully masculinized with respect to dancing and RA neuron soma size and density, and were partially masculinized with respect to song nuclei volumes and singing. Treatment beginning after week 1 was ineffective or less effective for all measures. Only for RA neuron measures was treatment for all three weeks more effective than week 1 treatment. Thus the first post-hatching week is the most influential period of those tested for effects of exogenous estrogen on sexual differentiation in this species, and is a period during which both masculinization of females and demasculinization of males is possible. 1994 John Wiley & Sons, Inc.     

Sexual isolation in Drosophila. II. Intraspecific variation in mate recognition systems

A simple behavioral model is used to investigate whether differences in the specific-mate-recognition system (SMRS), occur within species of the Drosophila genus. This model takes into account, and overcomes, the distorting effect of vigor differences on experimental results. Analysis shows significant deviations from the expected values under the assumption of identical SMRSs in around one fifth of the multiple-choice experiments performed with natural strains of twelve different Drosophila species. Different selection procedures raise the number of significant assortative mating results between strains of D. melanogaster and D. pseudoobscura from 3.0% to 32.8%. Finally, sub- or semispecific taxa show variations in their SMRS even more frequently (74.5%). Differences in male vigor and female receptivity are also found. These results show that a classification of Drosophila species based on SMRS stability, as proposed by the “Recognition concept of species”, is virtually impossible.     

Attraction of the sexes inFormica lugubris Zett (Hymenoptera: Formicidae)

Summary Sexuals ofFormica lugubris fly to mating places, where females attract males by using a sex pheromone. Females collected on the nest surface before departing on a mating flight are much less attractive than those collected on the mating place after the mating flight, suggesting that the mating flight triggers the release of the sex pheromone. Olfactory cues are essential for males to locate females while they patrol. Males probably use visual cues to locate females once they have alighted nearby them. Males are also attracted by aggregations of other males on the ground, probably because one or several females are likely to be close to male aggregations.     

FEMALE REPRODUCTIVE EFFORT DEPENDS ON THE DEGREE OF ORNAMENTATION OF THEIR MATES

Sexual selection theory assumes that secondary sexual characters do not influence female reproductive effort. Female animals may invest relatively more in reproduction if they acquire mates of high phenotypic quality, because offspring sired by preferred males may be relatively more viable than offspring sired by less preferred males. Here we report for the first time in a field study that females of the monogamous barn swallow Hirundo rustica adjust their reproductive effort to the attractiveness of their mates. Experimental manipulation of male tail length, which is a trait currently subject to a directional female mating preference, affected the reproductive effort by females in single broods as well as their decision on the seasonal number of clutches. These results, and those of previous experiments, demonstrate that female barn swallows assess the quality of their mates throughout the reproductive season and adjust their reproductive decisions accordingly. This result has important implications for the theory of sexual selection and for the possibility of testing current models of female mate preferences, because the viability of offspring will be confounded by differential reproductive effort.     

Effects of sexual differences of age at maturity and survival on population sex ratio

Summary Five demographical factors influencing the sex ratio of a population are classically considered. The influence of two of them is dependent on the longevity of individuals in the population. The effect of differential age at maturity between males and females is higher for animals with low annual survival, whereas the effect of differential annual survival between males and females is higher for animals with high annual survival. Such a conclusion applied to turtles, which are long life-span animals, allows us to retain differential survival between sexes as a major factor influencing the population sex ratio.