Differential elevational cline in the phenology and demography of two temporally isolated populations of a damselfly: Not two but one taxon?

1. Temporal isolation by cohort splitting is a life‐history mechanism that has been reported in many temperate insects, including those inhabiting freshwater habitats. Although the cohorts seem to maintain separate temporal niches in a specific location, the temporal isolation may be disrupted across a geographic gradient due to constraints imposed by seasonality. 2. This prediction was tested on two temporally isolated populations of the obligatory univoltine Lestes virens (Odonata, Lestidae) in north‐east Algeria. Although the two cohorts emerge at the same time in spring, one cohort reproduces in summer, while the second cohort estivates in summer and reproduces in autumn. A survey assessing the phenology and abundance was conducted on eight ponds across an elevational gradient (5–1012 m asl) using capture–mark–recapture and adult density sampling. 3. In all sites from low to high elevation, the species showed cohort splitting. The phenology of reproduction of both cohorts showed a delay with elevation, but the cline was 2.2 days for the summer cohort and 0.7 days for the autumn cohort per 100 m of elevation. Moreover, the density of adults in the autumn cohort was higher than that of summer cohort across the entire elevational range, and the difference increased with elevation. 4. These findings regarding the differential elevational cline in the phenology show that the temporal isolation of the two cohorts becomes narrower at high elevation, suggesting potential inter‐cohort temporal overlap at higher elevations. 5. The claim that the two cohorts of L. virens are true temporally isolated species needs further investigation.     

Aspects of Reproductive Biology of the Scalloped Hammerhead Shark, Sphyrna Lewini, off Northeastern Brazil

Ninety four scalloped hammerhead sharks, Sphyrna lewini (53 females and 41 males) ranging in size from 121 to 321cm total length (TL), were collected from surface gillnetters operating off northeastern Brazil and throughout the southwestern equatorial Atlantic Ocean between January and December 1996. A common regression for TL and eviscerated weight (EW) was calculated as, logEW = –11.786 + 2.889 logTL. Females and males were categorised into reproductive stages (4 and 2, respectively) according to morphological changes in their gonads. Size at sexual maturity for females was estimated to be 240cm, while males appeared to mature at between 180 and 200cm. Gravid females had between 2 and 21 embryos or pups, varying in TL from 3 to 38cm. There was no relationship between maternal length and size of litter. Copulation and parturition appear to occur outside the sampled area and possibly closer to the coast. With the exception of slightly lower uterine and ovarian fecundities, the results support the few existing data on the reproductive cycle of S. lewini in other areas.     

中黑盲蝽羽化节律及交配行为初步研究

在光周期L∶D=16∶8,温度(25±1)℃条件下对中黑盲蝽Adelphocoris suturalis Jakovlev羽化规律及交配行为进行观察,结果表明:中黑盲蝽雌、雄成虫全天均可羽化,雌虫羽化高峰出现在亮灯后7:00—9:00am,雄虫的羽化高峰出现在亮灯后5:00—7:00am;羽化过程历时较短,仅5～7 min。成虫自4日龄开始达到性成熟;室内短距离条件下雌虫通过足摩擦腹部(有时会伴随着振翅)吸引雄虫,同时雄虫用足摩擦腹部并振动翅膀回应雌虫,定位雌虫后发生交配,交配时间约30 s。     

Polymorphic fundatrices in thimbleberry aphid — ecology and maintenance

The thimbleberry aphid,Masonaphis maxima (Mason) lives on patches of plants that support 3,4 or 5 generations depending on site and weather. The life cycle requires sexual females and males to produce overwintering eggs. The eggs hatch in the spring to produce the first ’fundatrix’ generation; subsequent generations are produced parthenogenically. Males and other morphs are produced by wingless virginoparae, but sexual females are produced by ’gynoparae’, a winged morph that is specialized to produce only sexual females. The fundatrices have no indication of the number of generations that the plants will support in the current year. There are two fundatrix types that coexist in different ratios depending on the number of generations supported by the patch the previous year. One type produces sexual females in generations 3 and 5, and males in generations 4 and 5; the other type produces sexual females in generations 4 and 5, and males in generations 3, 4 and 5. The dimorphism adapts the aphid to its heterogeneous and somewhat unpredictable environment. The role of sex in the maintenance of the dimorphism is discussed. This is the first report of fundatrix polymorphism and consequent differential sex expression in aphids.     

Optimal time to patency in parasitic nematodes: host mortality matters

We develop an optimality model based on classical epidemiological models to investigate the optimal time to patency in parasitic nematodes in relation to host mortality and parasite mortality. We found that the optimal time to patency depends on both host longevity and prepatent mortality of nematodes. We tested our models using a comparative analysis of the relationships between nematode time to patency, nematode mortality and host mortality. Although we confirmed the importance of prepatent mortality, we also found a significant positive influence of host mortality. Host mortality rate affects parasite survivorship and life history strategies in the same way that habitat-specific mortality regimes drive the evolution of life histories in free-living organisms.     

Male reproductive polymorphism and form-specific habitat utilization of the damselflyMnais pruinosa (Zygoptera: Calopterygidae)

Habitat utilization patterns were studied in damselfly males,Mnais pruinosa, which have two male forms with different reproductive behaviors. The ‘esakii’ (orange-winged males) were territorial around oviposition sites, while the ‘strigata’ (hyaline-winged males) were non-territorial, often sneaking into theesakii's territory or loitering on the foliage of vegetation along stream banks. The place in the stream in the study area where females frequently appeared was covered by reeds and had abundant oviposition sites. It was difficult for the territorialesakii to stay there because the crowded reeds prevented them from defending their territory and discovering the females. Furthermore, there was competition for the limited territorial space with another species,Mnais nawai. Strigata males concentrated in this place in direct proportion to the number of females. Females frequently mated withstrigata males and probably deposited eggs fertilized bystrigata sperm rather thanesakii sperm. The density ofstrigata was higher than that ofesakii in this study area. If the average reproductive success ofesakii andstrigata males is equal, this may indicate that the equilibrious point between the two male forms is biased towardstrigata.     

Optimal timing of first reproduction in parasitic nematodes

The time between infection and the onset of reproduction (maturation time) is a key determinant of body size, fecundity and generation time in parasitic nematodes. An optimality model for maturation time is developed centred on prematurational growth, the duration of which has opposing consequences for fecundity and for survival to reproductive age. The maturation time favoured by natural selection is found to be inversely proportional to prematurational mortality rate. The product of maturation time and mortality rate is predicted to be an invariant number equal to the allometric slope linking daily fecundity to maturation time. Predictions are tested using comparative data on mammalian gastrointestinal nematode taxa. Half the cross-species variation in prepatent period (the time from infection until propagules are shed from the host) is accounted for by this adaptive trade-off hypothesis, even though many biological details are not explicitly modelled. These results are discussed in the light of previous studies and in the context of general models of life history evolution.     

Evolution of pleiotropic alleles for maturation and size as a consequence of predation

Understanding life-history evolution requires knowledge about genetic interactions, physiological mechanisms and the nature of selection. For platyfish, Xiphophorus maculatus, extensive information is available about genetic and physiological mechanisms influencing life-history traits. In particular, alleles at the pituitary locus have large and antagonistic effects on age and size at sexual maturation. To examine how predation affects the evolution of these antagonistic traits, I examined pituitary allele evolution in experimental populations differing in predation risk. A smaller size, earlier maturation allele increased in frequency when predators were absent, while a larger size, later maturation allele increased in frequency when predators were present. Thus, predation favours alleles for larger size, at the cost of later maturation and reproduction. These findings are interesting for several reasons. First, predation is often predicted to favour early reproduction at smaller sizes. Second, few studies have shown how selection acts on alleles that affect age and size at sexual maturation. Finally, many studies assume that trade-offs between these life-history traits result from antagonistic pleiotropy, with alleles that positively affect one trait negatively affecting another, yet this is rarely known. This study unequivocally demonstrates that genetically based trade-offs affect life-history evolution in platyfish.     

Trade-off between age of first reproduction and survival in a female primate

Trade-offs are central to life-history theory but difficult to document. Patterns of phenotypic and genetic correlations in rhesus macaques, Macaca mulatta—a long-lived, slow-reproducing primate—are used to test for a trade-off between female age of first reproduction and adult survival. A strong positive genetic correlation indicates that female macaques suffer reduced adult survival when they mature relatively early and implies primate senescence can be explained, in part, by antagonistic pleiotropy. Contrasts with a similar human study implicate the extension of parental effects to later ages as a potential mechanism for circumventing female life-history trade-offs in human evolution.     

Adaptive sex-specific life history plasticity to temperature and photoperiod in a damselfly

We investigated four predictions about how temperature, photoperiod and sex affect the life history plasticity and foraging activity of a damselfly. (i) As predicted, increased temperatures increased foraging activity and growth rates, but in contrast with the prediction, late photoperiod (high time stress) did not affect foraging activity and growth rate. (ii) Unexpectedly, the increase in growth rate at increasing temperatures was not larger under high time stress. (iii) As predicted, age and size at emergence decreased at higher temperatures and at the late photoperiod. Temperature-induced life history shifts were direct or the result of behavioural growth mediation depending on the temperature range. Photoperiod-induced life history shifts were direct. (iv) As predicted, males emerged before females but at a smaller size. The degree of sexual size dimorphism was influenced by the joint effects of temperature and photoperiod. We could only detect genetic variation in size plasticity to photoperiod. The match between the sex-specific life history responses to temperature and photoperiod and predictions by relevant optimality models suggests adaptive life history plasticity to these variables.