Sexual size dimorphism, sex ratio and the relationship between seasonality and water quality in four species of Gordiida (Nematomorpha) from Catamarca, Argentina

A total of 687 adult nematomorphs of four species of Gordiida: Chordodes brasiliensis (393 specimens), Noteochorododes cymatium (47 specimens), N. talensis (162 specimens) and Pseudochordodes dugesi (85 specimens) were collected during a period of 1 year from El Simbolar stream, Argentina. Free-living worms were abundant during autumn and spring, but their number decreased during winter and summer. Males were shorter and significantly more abundant than females. The presence of N. cymatium, N. talensis and P. dugesi was correlated with water temperature and these species were most abundant in winter and spring. The presence of C. brasiliensis was correlated with flow rate and pH; this species was more abundant in autumn and winter. These four species are sympatric.     

Fitness consequences of alternative life histories in water striders,Aquarius remigis (Heteroptera: Gerridae)

Using field and laboratory observations and experiments over 3 years, I investigated whether reproductive trade-offs shape individual life histories in two natural populations of the water strider, Aquarius remigis, in which univoltine and bivoltine life cycles coexist. Both later eclosion dates and food shortages, even after adult eclosion, induced diapause in females, thus deferring reproduction to the following spring. Adult body size was positively affected by food availability during juvenile development. Higher food levels also increased the reproductive output of females, but not their longevity or oviposition period. When compared to spring breeders (univoltine life cycle), direct (summer) breeders (bivoltine life cycle) experienced reduced lifetime egg numbers and longevity, as well as reduced survivorship of their second-summer-generation offspring; these reproductive costs offset, at least in part, the advantage in non-decreasing populations of having two generations per year. Fecundity was correlated with body size, and among summer-generation females direct breeders were larger than non-breeders. The time remaining before the onset of winter and/or the time since adult eclosion augmented cumulative energy uptake, and consequently the lipid reserves and winter survival probability of non-breeding (diapausing) summer adults approaching hibernation. Overwintered spring reproductives died at faster rates than non-reproductive summer individuals despite greater food availability in spring, indicating a mortality cost of reproduction. Body length correlated with absolute and not with proportional lipid content but showed no consistent relationship with survivorship in the field. These results are in agreement with current theory on the evolution of insect voltinism patterns, and further indicate high degrees of life history flexibility (phenotypic plasticity) in the study populations in response to variable environmental factors (notably photoperiod and food availability). This may be related to their location in a geographic transition zone from uni- to bivoltine life cycles.     

Environmental correlates of life history pattern in ground-beetles on Tenerife (Canary Islands)

The spatial and temporal structure of Carabus (Nesaeocarabus) interruptus Dejean, 1831 populations and the independent effects of climate along altitudinal gradients in the island of Tenerife, especially whether environmental preferences constrains the species breeding patterns at local and regional scales were evaluated. Ground-beetles were sampled with twenty-one pitfall traps in each of the forty-one plots during one year study. Some sampled specimens were dissected and dried to determine sex, weight and ovarian maturation. The populations were restricted to the middle climatic zone (600–1700 m). There was a long adult activity period from October to June and the changes in the weekly capture success were strongly correlated with the rainfall and temperature. Overall the males during winter were more active than the females. The emergence of new adults occurred only in spring and the body dry weight peaked in April–May. From start of autumn the weight was recovered to the initial values of the cycle, increased and peaked in January. The females prolonged its oviposition period from mid-autumn to the starting of spring. The species showed a winter breeding pattern and the seasonal variations in multiple life history traits could correspond with the changing conditions of the microclimatic variables. An evolutionary ecological model could help explain the life history pattern variability among the Carabus species in South-western Europe. The species could tackle the geographic dispersion of their populations for the single purpose of seeking a suitable hydrothermal environment (high rainfall and mild temperatures) if the food was insured.     

Asynchronous male and female life cycles in the sexually dimorphic, harem-forming isopod Paragnathia formica (Crustacea: Isopoda)

The complex life history of the sexually dimorphic, harem-forming isopod Paragnathia formica Hesse is described, combining published information with new observations. The results of a two-and-a-half year field study, carried out within the animal's saltmarsh habitat, are presented, revealing significant differences in the life cycles of males and females. Settlement to the breeding habitat of final stage male and female larvae, derived from the same annual generation, was recorded at very different times of the year. The total lifespan of males was shown to be twice that of females.
The larvae, temporary ectoparasites of estuarine fish, and the non-feeding, burrow-living adults are described and categorized into several developmental phases, whose numbers were recorded during the course of the study.
The annual production of larvae during a limited period in the autumn, and the subsequent settlement of final stage larval females and males the following year, were monitored. Larval females entered the burrows of adult males in the spring to breed, and died after releasing viviparous broods in the autumn. Larval males settled later in the summer, reaching adulthood in the autumn and overwintering before breeding some 18 months after their birth and dying at the end of the breeding season. Adult males thus bred with females from the next generation. The differences in male and female life cycles led to great seasonal variations in adult sex ratios, a huge winter bias towards males contrasting with a brief excess of females in the summer.     

Study of the life cycle of Amblyomma dubitatum (Acari: Ixodidae) based on field and laboratory data

The life cycle of Amblyomma dubitatum was described based on the seasonal distribution of all parasitic stages and the development periods of engorged ticks under different conditions of photoperiod and temperature. All stages were found active along the entire year in the study area. Larvae peaked from May to July, nymphs peaked from July to October, and females peaked from November to March. This pattern represents a life cycle with one generation per year with most of the ticks reaching adulthood during the warmest months. The analysis of the effect of the photoperiod on the development of A. dubitatum showed no indication of morphogenetic diapause. Exposure of ticks to field conditions indicates a delay in metamorphosis of immature stages, in the oviposition of females and in the incubation of eggs, which were associated with low winter temperatures. The results indicate that though A. dubitatum has a one year life cycle, more than one cohort can co-exist within the same population in a certain interval of time. Finally, the potential role of small rodents as hosts for larvae and nymphs of A. dubitatum is confirmed.     

Prevalence of the Lyme disease spirochete in populations of white-tailed deer and white-footed mice

The prevalence of the Ixodes dammini spirochete (IDS) in white-tailed deer (Odocoileus virginianus) and white-footed mice (Peromyscus leucopus) was studied on the eastern end of Long Island, New York. Both species commonly occur in a variety of habitats, are preferred hosts of Ixodes dammini, and can harbor the spirochetes in the blood. Each animal was examined for spirochetemia, tick infestation, and IDS infection rates in the ticks that were removed from it. The results obtained suggest that in winter deer can be infected by questing adult I. dammini. Adult ticks apparently are infected through transtadial transmission of spirochetes from subadult ticks which had fed earlier in their life history on infected animals. Deer are important hosts of adult ticks and the IDS in winter and probably are a reservoir host in other seasons. The patterns of spirochete prevalence suggest that deer and mice are reservoirs of the organism and thus are fundamental to the ecology of Lyme disease on Long Island.     

Temporal shifts in the pair-bond dynamics of New Zealand robins (

Winter is a challenging time for temperate insectivorous songbirds, due to colder temperatures, reduced prey activity and shorter diurnal foraging times. For species that are non-migratory, territorial and monogamous, winter conditions may result in within-pair competition. However, little is known about how monogamous pairs coexist on their winter territories. We investigated temporal patterns in male?female interactions of the New Zealand robin (Petroica australis to better understand mechanisms of coexistence during winter. Previous work has shown that male robins are physically dominant over females and maintain priority access to food year-round. We quantified female behaviour throughout the 2008 non-breeding season to better understand how females coexist with physically dominant males on winter territories. Results showed that pairs rarely forage in close proximity in autumn and winter, suggesting females avoid males at this time of year. Males and females begin to spend more time foraging together as winter turns to spring. During this winter?spring transitional period, females steal large amounts of food hoarded by males. These results indicate that male and female New Zealand robins use different behavioural mechanisms to coexist on their winter territories. While males are dominant physically, females show a seasonally variable strategy where they avoid males in autumn and winter, and then steal male-made caches from early spring until the onset of inter-pair cooperation and the breeding season.     

Too hot to handle? Phenological and life‐history responses to simulated climate change of the southern green stink bug Nezara viridula (Heteroptera: Pentatomidae)

The effect of simulated climate change on Nezara viridula was studied close to the species' northern range limit in Japan. Insects from the same egg masses were reared for 15 months in 10 consecutive series under quasi‐natural (i.e. outdoor) conditions and in a transparent incubator, in which climate warming was simulated by adding 2.5 °C to the outdoor temperature. The warming strongly affected all life‐history and phenological parameters. In the spring, the simulated warming advanced the timing of postdiapause body colour changes and reproduction. In the early summer, it increased egg production and accelerated nymphal development. In the late summer (the hottest season), the effect of the simulated warming was strongly deleterious: nymphs developed slowly, suffered higher mortality and had difficulties during final moulting; the emerged females were smaller, some exhibited abnormal cuticle, produced fewer eggs and had a decreased life span. In the autumn, the warming accelerated nymphal development, resulted in larger female size, affected the timing of the diapause‐associated adult body colour change from green to russet and enhanced preparation for overwintering. Larger females had higher winter survival rate than smaller females. The warming strongly increased survival rate in both size classes and allowed smaller females to reach the same winter survival rate as larger females had under the quasi‐natural conditions. The winter survival also differed between the green and dark‐coloured females under the quasi‐natural, but not under the warming conditions. However, under the warming conditions, green females survived the winter even better than dark‐coloured females did under the quasi‐natural conditions. The warming also shortened the life span of females from the summer generations and prolonged it in those from the autumn generation. It is concluded that even a moderate temperature increase (+2.5 °C) in the future is likely to have a complex influence upon insects, strongly affecting many of their life‐history and phenological parameters.     

Density-dependence vs. density-independence - linking reproductive allocation to population abundance and vegetation greenness

1. Recent studies have shown that optimal reproductive allocation depends on both climatic conditions and population density. We tested this hypothesis using six years of demographic data from eight reindeer (Rangifer tarandus) populations coupled with data on population abundance and vegetation greenness [measured using the Enhanced Vegetation Index (EVI)]. 2. Female spring body mass positively affected summer body mass gain, and lactating females were unable to compensate for harsh winters as efficiently as barren ones. Female spring body mass was highly sensitive to changes in population abundance and vegetation greenness and less dependent on previous autumn body mass and reproductive status. Lactating females were larger than barren females in the spring. Moreover, female autumn body mass was positively related to female autumn body mass and reproductive success and was not very sensitive to changes in vegetation greenness and population abundance. 3. Offspring autumn body mass was positively related to both maternal spring and autumn body mass, and as predicted from theory, offspring were more sensitive to changes in vegetation greenness and population abundance than adult females. A lagged cost of reproduction was present as larger females who were barren, the previous year produced larger offspring than equally sized females that successfully reproduced the previous year. 4. Reproductive success was negatively related to female autumn body mass and positively related to female spring body mass. Moreover, females who successfully reproduced the previous year experienced the highest reproductive success. The fact that negative density-dependence was only present for females that had successfully reproduced the previous year further support the hypothesis that reproduction is costly. 5. This study shows that female reindeer buffer their reproductive allocation according to expected winter conditions and that their buffering abilities were limited by population abundance and a lagged cost of reproduction and enhanced by vegetation greenness.     

The reproductive cycle and life history of the Arctic copepod Calanus glacialis in the White Sea

Seasonal variations in the gonad development and sex ratio of copepodite stage V (CV) and adults were examined from February to November in order to understand the reproductive cycle and the life history of Calanus glacialis in the White Sea. Gonad maturation, sexual differentiation and moulting to adults take place during the 2nd year of development. Energy accumulation takes place in the spring and summer of the 2nd year. The following autumn/winter is the major period of CV maturation, which occurs independent of food supply. Maturation of males precedes that of females by 2–3 months. The maximum proportions of CV and adult males are found in the population in October and November. The onset of female maturation is observed in February and March, ca. 2 months prior to the spring phytoplankton bloom. Reproduction takes place between April and June. Its termination in the second half of June coincides with the warming of the surface water layer where egg laying takes place. Variations in the gonad morphology throughout the year suggest long life spans and iteroparity of females of C. glacialis in the White Sea. Many of them survive for several months after reproduction and are able to overwinter again. Therefore, females with different life histories co-occur in the population in winter: “young” females recently moulted from the overwintering CVs, and “old” females which have spawned at least once in their life, after which they return to overwintering conditions. In contrast, males have shorter life spans of 3–4 months resulting in a sex ratio skewed toward females at all seasons. Accepted: 27 April 1999     

Some aspects of overwintering in southern England of the mosquitoes Anopheles atroparvus and Culiseta annulata (Diptera: Culicidae)

Abstract. 1. Overwintering of the mosquitoes Anopheles atroparvus van Thiel and Culiseta annulata Schrank, both of which feed on blood throughout the year, is compared.
2 The aquatic stages, males and gonoactive females of A.atroparvus disappear before winter, leaving a generation of inseminated, nulliparous, diapausing females to overwinter. Blood meals taken by diapausing females merely serve to maintain fat reserves. After re-activation in March–April, gonoactive life expectancy appears to be rather short. Aquatic development at this season is slow and eggs laid in the spring do not significantly affect adult densities until June.
3. Aquatic stages, males and gonoactive females of C.annulata are present throughout the year. This species appears to be able to overwinter without recourse to diapause, females passing the winter in alternating, or lasting, states of cold-induced quiescence or normal gonoactivity.     

Influence of environmental factors on the occurrence of Ixodes ricinus ticks in the urban locality of Brno - Pisárky, Czech Republic.

The occurrence of Ixodes ricinus ticks was observed in the suburban locality of Brno-Pisárky (South Moravia, Czech Republic) from March to November, 1996 to 2002. A total of 2,813 ticks was collected. Statistical tests divided the activity of ticks into three periods during the year. The curve of seasonality had two peaks with a maximum in May and August, with a significantly larger number of specimens collected during this period compared to other months. The abundance of ticks during Spring and Autumn months was comparable. All developmental stadia of ticks were found in this locality. The number of larvae, males, and females was not significantly different, but the occurrence of nymphs was significantly greater. Except for the year 2000, there were no statistically significant differences in tick abundance. Tick activity was not dependent on humidity but did vary directly with temperature. This relation had a linear character and could be described by the equation y = 8.3 + 1.8x.     

Rhipicephalus sanguineus: Observations on the parasitic stage on dogs in the Negev Desert of Israel

Sixteen dogs were studied for infestation with R. sanguineus in Kibbutz Ze'elim in the north-western part of the Negev Desert over a period of one year. The mean number of ticks per dog per month was 16.4. The majority of the ticks were adults: males (48.6%) and females (34.4%). The cars and abdomen of the dog were the predilection sites for the ticks. Male ticks were more abundant on the ears, whereas female ticks were more abundant on the ears and the abdomen. A strong correlation between tick numbers and the ambient temperatures was found. The mean percentage of dogs infested in the winter months was 16.6% and increased in the summer months to 34.4%. During winter, ticks were found more often on the ears and head of their hosts whereas in summer they were distributed mainly on the ears, headd and abdomen. The male: female ratio was higher in winter (2.3:1) than in summer (1.1:1).     

High cold tolerance through four seasons and all free-living stages in an ectoparasite

Off-host stages of temperate parasites must cope with low temperatures. Cold tolerance is often highest in winter, as a result of diapause and cold acclimation, and low during the active summer stages. In some blood-feeding ectoparasites, offspring provisioning determines cold tolerance through all the non-feeding, off-host stages. Large size increases survival in the cold, but so far seasonal variation in within-female offspring size has not been associated with offspring cold tolerance. The deer ked (Lipoptena cervi) reproduces on cervids from autumn to spring. Newborn pupae drop off the host, facing frosts without any acclimation. We examined cold tolerance through 4 seasons and from birth to adulthood by means of short- and long-term frost exposure. We expected females to produce more tolerant offspring in winter than in spring. Large spring pupae survived prolonged frosts better than did small winter pupae. Thus more tolerant offspring were not produced when the temperature outside the host is at its lowest. Unexpectedly, the freezing points were -20 °C or below all year round. We showed that high cold tolerance is possible without acclimation regardless of life stage, which presumably correlates with other survival characteristics, such as the starvation resistance of free-living ectoparasites.     

Sex ratio in ixodid tick collections from Leningrad Province

The analysis of results of many-year regular collections of ixodid ticks has shown that females (56%) were dominant in I. persulcatus while in I. ricinus were dominant males (52%). The ratio between sexes in both species changed noticeably as in individual years so during the imago activity season. In summer collections of I. lividus females were dominant every year, the share of which accounted on the average for 70% and varied from 69 to 75% within different seasons and from 60 to 83% within imago activity season. During hibernation and in spring the share of males and females was nearly adequate.     

Short Communication Seasonal distribution of Rhipicephalus sanguineus ticks (Acari: Ixodidae) on dogs in an urban area of Morelos, Mexico

Between 1993 and 1995, we examined 1742 dogs at two veterinary clinics in Cuernavaca City in Mexico for the presence of Rhipicephalus sanguineus ticks. The overall tick infestation prevalence was 20% and there were no significant differences (p > 0.05) between different years. The prevalence was somewhat higher in spring, summer and autumn (20% or more) than in winter (13.7%). A positive correlation (p < 0.01) was found between prevalence of ticks and rainfall in spring, summer and autumn, whereas in winter there was only a correlation with temperature. Different stages of the tick were found and it was calculated that 2.5 generations could be completed each year. It is concluded that the enviromental conditions of Cuernavaca City favour development and maintenance of R. sanguineus ticks throughout the year and that its role as a vector of diseases poses a threat to dogs and may have potential zoonotic risks. © Rapid Science Ltd. 1998     

Mating and behavioural diapause inIxodes ricinus L.

This study established that in an open rough-grazing habitat in Ireland a large proportion of female ticks mated in the vegetation rather than on the host, confirming observations made by other workers in scrub and forest habitats in Switzerland and Russia. It was found that many ticks active from October onwards had already mated even though they were moulted and apparently derived from the spring population. This activity was at odds with theview that such ticks are prevented from becoming active in autumn by a behavioural diapause. Laboratory and plot experiments involving observations on questing activity and feeding showed that the behavioural diapause of females was abolished by exposure to males. Male ticks did not show a behavioural diapause. In areas of high tick density this mechanism could result in the transfer of ticks from spring to autumn populations and, since the mortality rate of the autumn population is higher, could also contribute to density-dependent population regulation.     

Population structure and dynamics of sympatric Apodemus species (Rodentia: Muridae)

This paper describes the population biology of sympatric populations of Apodemus sylvaticus and A. flavicollis in western England. Annual changes in population siie closely resembled those seen in allopatric populations such that simultaneous peaks in number occurred only in autumn and early winter. Numbers of A. sylvaticus were low and stable in early summer increasing rapidly in late summer and autumn and remaining high throughout winter before a sharp decline in spring. Numbers of A. flavicollis increased after the start of reproduction and continued to rise throughout summer and autumn. The period of major decline of this species was during early winter. Densities of A. sylvaticus and A. flavicollis were comparable with those cited in allopatric studies. Spring populations of both species consisted of cohorts first appearing in the late summer and autumn of the previous year. Few individuals present in spring survived the summer. Reproduction of A. flavicollis commenced four to six weeks before that of A. sylvaticus . Seasonal variation in mean weight of adult males and females also indicates that those changes, due to the acquisition of secondary sex characteristics and reproductive maturity, occur earlier in A. flavicollis than in A. sylvaticus . Data presented contain no evidence of interspecific competition and it is concluded that interspecific differences, chiefly asynchrony in reproduction and annual population cycles, contribute to their stable coexistence.     

The life history of the minnow Phoxinus phoxinus (L.) in a productive stream

SUMMARY. 1. In the River Frome, Dorset, this small cyprinid spawned from mid-April to early August and consequently some 0 group minnows did not develop scales until the following spring.
2. Most I group fish formed a summer hyaline band on their otoliths in a edition to the normal winter band.
3. Life-span was short with a winter age-structure of 67% 0 group, 32% I group and 1% II group fish with mean fork lengths of 29, 55 and 73 mm respectively.
4. In June, substantial numbers of I group fish reached reproductive size (50mm) and thereafter progressively replaced II group fish in the spawning shoals. Few II group males survived beyond June, few females beyond August.
5. Only half of I group minnows reached matutity. These were usually fish which had reached 30mm by the previous winter. Very few of these large I group fish survived to spawn the following year.
6. This differential mortality, together with the loss of condition and disappearance of II group fish during spawning, may indicate the cost of an extended high level of reproductive effort.
7. In this productive environment the life history of the minnow more closely resembles that of the small sympatric species Cottus gobio and Noemacheilus harhatulus than it does that of sympatric cyprinids.