Emergence of some caddisflies (Trichoptera) from a wooded stream in southern Ontario

Twenty-eight species of nine families of caddisflies (Trichoptera) were identified in 170 samples taken over an 8-month period from five emergence traps placed on a second-order, forested, cold-stenothermal stream on the Niagara Escarpment, Ontario, Canada.A mean of 980.9 caddisflies m^–2 of streambed was obtained over the entire sampling period. Eleven common species accounted for 92.8% of the total emergence with specific proportions ranging from 23.8% (Wormaldia moesta) to 0.11 % (Rhyacophila sp.). The use of various kinds of traps in other studies and their effects on the detection of species composition and abundance are discussed and compared with the present study.Although the distributions of all the common species were invariant over time, four species showed low to high degrees of patchiness in the streambed; the other seven common species were uniformly distributed. However, a large residual variance suggested a subtle mechanism of microhabitat selection by the larvae and (or) pupae, not detectable by even the small emergence traps used.Both sexes of 15 species, only males of 4 and only females of 9 species were collected. Eight of the eleven common species showed significant departures from a balanced sex ratio and five exhibited a protandry of from 1 to 3 weeks. Neither this study nor others have been able to establish a predictable pattern of sex ratios in Trichoptera.The emergence periods and patterns of the eleven common species are described and compared with other studies. Of these common species, one emerged in the spring, seven during the summer and three during the late summer or early fall. Ten species had a short emergence period with a distinct peak and a significantly skewed pattern. One species,Parapsyche apicalis, exhibited a prolonged emergence period, no distinct peak and a significantly platykurtotic² pattern. With the exception ofLepidostoma sp. A, the emergence patterns of the common species were unimodal.     

THE INTERACTION PHENOTYPE IN THE DROSOPHILA WILLISTONI–SPIROPLASMA SYMBIOSIS

Both the population and coevolutionary dynamics of hereditary male-lethal endosymbionts, found in a wide range of insect species, depend on host fitness and endosymbiont transmission rates. This paper reports on fitness effects and transmission rates in three lines of Drosophila willistoni infected with either male-lethal spiroplasmas or a spontaneous nonmale-lethal mutant. Overall fitness measures were reduced or unaffected by the infection; however, some infected females produced more offspring in early broods. Maternal transmission rates were high, but imperfect, and varied with a female's age, host line, and spiroplasma type. No evidence for paternal or horizontal transmission was found. If an altered temporal pattern of reproduction is not a factor in countering the loss of spiroplasma hosts through imperfect maternal transmission, persistence of this endoparasitism remains unexplained. Tolerance of the infection and ability to transmit bacteria varied with both host and spiroplasma line. Analysis of the interaction between the spontaneous nonmale-lethal mutant and its host suggests this symbiosis has undergone coevolution under laboratory culture.     

Endocrine correlates of intra-specific variation in the mating system of the St. Peter's fish (Sarotherodon galilaeus)

The Challenge Hypothesis postulates that androgen levels are a function of the social environment in which the individual is living. Thus, it is predicted that in polygynous males that engage in social interactions, androgen levels should be higher than in monogamous animals that engage in parental care. In this study, we tested this hypothesis at the intra-specific level using a teleost species, Sarotherodon galilaeus, which exhibits a wide variation in its mating system. Experimental groups of individually marked fish were formed in large ponds with different operational sex-ratios (OSR) to study the effects of partner availability on blood plasma levels of sex steroids [11-ketotestosterone (11-KT), testosterone (T), and 17,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P)] and gonadosomatic index (GSI). Polygyny mostly occurred in the female biased OSR groups. 17,20beta-P and gonadosomatic index did not differ among OSR groups. However, 11-KT was high in male biased OSR and positively correlated with aggressive challenges, thereby supporting the central postulate of the Challenge Hypothesis. The results of T were the inverse of those of 11-KT, probably because 11-KT is metabolized from T. 11-KT levels of polygynous males did not differ neither from those of monogamous males, nor from those of males that participated in parental care. These results do not support the expected relationships between polygyny, parental care, and androgen levels. The differences from expectations for 11-KT may be related to the fact that in S. galilaeus, the mating and the parenting phase are not clearly separated and thus, males may still fight and court while they are brooding.     

Local sex-ratio dynamics: a model for the dioecious liverwort Marchantia inflexa

In many dioecious bryophyte species, population sex ratios range from all female to all male. The focal species of the present study, the liverwort Marchantia inflexa, forms patches on rock and bark surfaces, and these differ widely in sex ratio at a rainforest field site in Trinidad. This analysis – to our knowledge the first modeling study of sex-ratio dynamics in a dioecious clonal organism – addresses abundances of male and female M. inflexa through time within an individual patch. We represent the life history of this species using seven different stages (non-reproductive, asexually reproductive, sexually reproductive males, non-reproductive, asexually reproductive, unfertilized and fertilized sexual females) and express their dynamics using ordinary differential equations. Some of the stages become more abundant as thalli extend over the substrate and may overgrow each other to capture space. Our simple representation of dynamics within the patch failed to stabilize the sex ratio: females gradually eliminated males at low to moderate disturbance frequency and males eliminated females at high disturbance frequency. This pattern did not hinge on whether sexual propagules could germinate within the patch, but asexual reproduction (via gemmae dispersed within the patch) played an important role. This suggests that the maintenance of sex in these populations may hinge on metapopulation structure and dynamics. Though sexual reproduction appears to be unimportant within patches, spores provide the primary means of recolonizing patches eliminated by large-scale disturbances. We found that shortly after the patch was fully occupied, the production of these wind-dispersed spores was maximized, but spore production declined thereafter as the sex ratio became increasingly biased toward one sex or the other. Much additional modeling and empirical work is needed to link within-patch dynamics across patches and account for dynamics at the metapopulation level.     

Effects of endosymbiotic Wolbachia on the diapause in Trichogramma hosts and effects of the diapause on Wolbachia

Abstract Used as an agent in biological control, Trichogramma which has been infected by endosymbiotic bacteria belonging to the genus Wolbachia and inducing the thelytokous mode of reproduction, increases rearing productivity in commercial insectaries. These insectaries can now make use of Trichogramma diapause to spread out and optimise their production. We therefore studied the effect of Wolbachia on the diapause in Trichogramma evanescens. The symbionts show no beneficial or harmful effect on the proportion of emergence in diapausing individuals or on their fecundity. Therefore, infected strains can easily be used in crop protection. On the other hand, low temperatures exert a slightly negative effect on Wolbachia, as detected from the proportion of females in the offspring of symbiotic diapausing females.     

EVOLUTION OF DRIVING X CHROMOSOMES AND RESISTANCE FACTORS IN EXPERIMENTAL POPULATIONS OF DROSOPHILA SIMULANS

Sex-ratio drive is a particular case of meiotic drive, described in several Drosophila species, that causes males bearing driving X chromosome to produce a large excess of females in their progeny. In Drosophila simulans, driving X chromosomes and resistance factors located on the Y chromosome and on the autosomes have been previously reported. In this paper, we report the study of the dynamics of sex-ratio factors in experimental populations. We followed the evolution in frequency of driving X chromosomes in the absence of resistance factors and the evolution of resistance factors in the presence of driving X chromosomes. The driving X chromosome was lost, contrarily to theoretical expectations that predict its rapid invasion. Autosomal resistances increased in frequency, and resistant Y chromosomes invaded the population very quickly, as predicted by theoretical models. Fitness measurements showed that the loss of the driving X chromosome was due to a strong deleterious effect that was expressed only when distorting males were in competition with standard males. However, the spread of autosomal resistances reduced this deleterious effect. Implications for the maintenance of polymorphism in natural populations are discussed.     

Sex ratio, mating behaviour and Wolbachia infections in a sheetweb spider

The solitary sheetweb spider Pityohyphantes phrygianus has a female-biased primary sex ratio. Earlier studies have indicated that female post-copulatory position may influence the degree of bias, but the adaptive significance of the departure from a Fisherian 1 : 1 sex ratio is not known. In this study we show that there is a significant relationship between abdominal position and offspring sex ratio in undisturbed females. Moreover, female mating behaviour (and thus sex ratio) is correlated with female size, but this relationship may shift from negative to positive depending on the presence of the maternally acquired endosymbiotic bacterium Wolbachia in both sexes. A survey of wild-caught individuals shows that the incidence of Wolbachia infection in natural populations is high. This indicates that Wolbachia may be a significant factor influencing female post-copulatory behaviour and sex ratio in natural populations. We discuss various adaptive reasons for sex-ratio bias and behavioural plasticity in females.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 181–186.     

Biology ofEpidinocarsis [=Apoanagyrus] lopezi [Hymenoptera: Encyrtidae] an exotic parasite of cassava mealybug,Phenacoccus manihoti [Homoptera: Pseudococcidae] in Nigeria

The biology ofEpidinocarsis (=Apoanagyrus) lopezi (DeSantis) was studied under fluctuating laboratory conditions of 24–31°C and 79–90% R.H. It is a solitary internal parasite. There are 4 tailed larval instars. The total developmental time from egg to adult ranged from 11–25 days, average 18 days. The duration of each developmental stage was: egg 2 days, 1 st instar 1 day, 2nd instar 1 day, 3rd instar 2 days, 4th instar 2 days, prepupa 4 days and pupa 6 days. Males mated several times, females mated once. Mated females produced both males and females, unmated females produced only males. Mated ovipositing females lived for 13 days while non-ovipositing mated females lived for 25 days. Parasitization decreased with increasing host density from 30% at a density of 10 hosts/plant/female to 11% at a density of 50. There was virtually no pre-oviposition period. Based on 10 females, the highest mean daily progeny production was 10. Females have an average oviposition period of 11 days and an average of 67 adult progeny. The sex-ratio was 1∶2.3 in favour of females.     

Reproductive biology of Mystus vittatus (Bloch) (Bagridae: Siluriformes) from Guntur,Andhra Pradesh

Maturation, minimum length at first maturity, spawning season, spawning periodicity, sex-ratio and absolute fecundity of Mystus vittatus, a common bagrid catfish, have been investigated. The observations show that spawning takes place during September and October. Each individual spawns only once in the season as evidenced by the study of the intraovarian ova. Females dominate the catches, and absolute fecundity (F) can be expressed by% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabaGaaiaacaqabeaadaqaaqaaaOabaeqabaGaciiBai% aac+gacaGGNbGaaeiiaiaabAeacaqGGaGaaeypaiaabccacaqGTaGa% ae4maiaab6cacaqGYaGaaeyoaiaabkdacaqGGaGaae4kaiaabccaca% qG0aGaaeOlaiaabgdacaqG3aGaaeymaiaabgdacaqGGaGaaeiBaiaa% b+gacaqGNbGaaeiiaiaabYeaaeaacaqGHbGaaeOBaiaabsgacaqGGa% GaaeOraiaabccacaqG9aGaaeiiaiaab2cacaqGXaGaaeOlaiaabwda% caqG0aGaaeinaiaabwdacaqGGaGaae4kaiaabccacaqGWaGaaeOlai% aabMdacaqG0aGaae4naiaabkdacaqGGaGaae4vaaaaaa!5FCC!\[\begin{gathered} \log {\text{ F = - 3}}{\text{.292 + 4}}{\text{.1711 log L}} \hfill \\ {\text{and F = - 1}}{\text{.5445 + 0}}{\text{.9472 W}} \hfill \\ \end{gathered} \]