Effects of two acanthocephalan parasites on the fecundity and pairing status of female Gammarus pulex (Crustacea: Amphipoda)

Acanthocephalan parasites are known to alter the reproductive biology and physiology of their hosts in various ways. In this study we investigated the influence of two acanthocephalan parasites, Pomphorhynchus laevis and Polymorphus minutus, on the fecundity and pairing success of female Gammarus pulex. The results show that P. laevis and P. minutus affect female intermediate host reproduction in different ways. Females infected with P. minutus were totally castrated, whereas those infected with P. laevis only showed reduced fecundity. The oocytes of P. laevis-infected females showed a similar structure to those of uninfected females, although infected females had a higher proportion of oocytes that had failed to reach complete maturity. In comparison, the oocytes of P. minutus-infected females demonstrate a clearly altered structure that suggests a major disruption to the process of vitellogenesis. In the field, males paired more frequently with uninfected females than with infected ones, and is a stronger effect for P. minutus-infected females than P. laevis-infected females. We suggest that the difference in pairing success of P. minutus-infected and P. laevis-infected females is a direct result of the different effects that the two parasites have on female fecundity.     

Distribution and microhabitats of native and non-native gammarids (Amphipoda, Crustacea) in Brittany, with particular reference to the endangered endemic sub-species Gammarus duebeni celticus

Aim  To assess temporal changes in gammarid distribution in Brittany and microhabitat-use overlap between the endangered endemic Gammarus duebeni celticus Stock & Pinkster, 1970 , the expanding natives G. pulex (Linnaeus, 1758) and Echinogammarus berilloni (Catta, 1878), and the introduced G. tigrinus Sexton, 1939.
Location  Brittany and adjacent regions in western France.
Methods  The spatial and temporal patterns in distribution of gammarids at the scale of Brittany were studied using 351 sites. Longitudinal distributions (from the source to the estuary of the river) and microhabitat-use (substratum type and water velocity) were also considered in selected rivers.
Results  At the regional scale, all species occurred together less often than expected statistically, with significant deviations from expected for G. pulex vs. both G. duebeni celticus and G. tigrinus , and for E. berilloni vs. both G. duebeni celticus and G. tigrinus . However, at the microhabitat scale, E. berilloni occurred significantly more often than expected with the endemic G. duebeni celticus , and this appears to be due to similar substratum and water velocity preferences, although at both the regional and microhabitat scales E. berilloni prefers wider streams than G. duebeni celticus . This study reveals a decline in the endangered G. duebeni celticus since 1970.
Main conclusions  The longitudinal and local distributions of G. duebeni celticus , and the higher-than-expected co-occurrence of the species with G. pulex , suggest that the decline of the endemic species may be due to changes in the environment and/or interference from native G. pulex , which is expanding its range in Brittany. The results are discussed as regards to the consequences for regional biodiversity.     

Interactive effects of elevated CO2 and temperature on the leaf-miner Dialectica scalariella Zeller (Lepidoptera: Gracillariidae) in Paterson's Curse, Echium plantagineum (Boraginaceae)

Doubling of the current atmospheric CO₂ concentration, and an increase in global mean annual temperatures of 1.5–6 °C, have been predicted to occur by the end of this century. Whilst the separate effects of CO₂ and temperature on plant–insect interactions have been examined in a number of studies, few have investigated their combined impact. We carried out a factorial experiment to explore the effect of a doubling of CO₂ concentration and a 3 °C temperature increase on the development of a complete generation of the leaf‐miner, Dialectica scalariella, in the host plant Paterson's Curse, Echium plantagineum. Elevated CO₂ increased biomass, reduced leaf N and increased C:N ratios in the host plants. Leaf thickness also increased under elevated CO₂, but only in the high‐temperature treatment. Female D. scalariella did not discriminate between plants grown at the different CO₂ levels when ovipositing, despite the reduction in foliage quality under elevated CO₂. Overall, the negative response of D. scalariella to elevated CO₂ was greater than for many species of free‐living insects, presumably because of the limited mobility imposed by the leaf‐mining habit. Development was accelerated at the high temperature and slowed under elevated CO₂. The net result was a reduction in development time of ～14 days in the elevated CO₂/high temperature treatment, compared to the ambient CO₂/low temperature treatment. Larval survivorship and adult moth weight were both affected by a significant interaction between CO₂ and temperature. At the low temperature, CO₂ had little effect on survivorship, but at the high temperature, survivorship was significantly reduced under elevated CO₂. Similarly, elevated CO₂ had a stronger negative effect on adult moth weight when combined with the high‐temperature treatment. A possible explanation for these results is that the high temperature accelerated insect development to such an extent that the larvae did not have sufficient feeding time to compensate for the poorer quality of the foliage. The frequency with which interactions between CO₂ and temperature affected both plant and insect performance in this study highlights the need for caution when predicting the effects of future climate change on plant–insect interactions from single‐factor experiments.     

The effects of controlled propagation on an endangered species: genetic differentiation and divergence in body size among native and captive populations of the Socorro Isopod (Crustacea: Flabellifera)

The endangered Socorro Isopod, Thermosphaeroma thermophilum, is endemic to a single thermal spring in Socorro, NM. This species is cannibalistic, with males more cannibalistic than females, and with females and juveniles more vulnerable than males as prey. In 1990, the New Mexico Department of Game and Fish, created the Socorro Isopod Propagation Facility (SIPF) near the natural habitat, Sedillo Spring (SS), to increase total population size and to examine the effects of habitat heterogeneity on population growth. We report the genetic and morphological effects of this experiment, using the natural population as a control. Captive subpopulations experienced bottlenecks of known intensity and duration, as well as different intensities of cannibalism. Using 57 AFLP markers, we show that in 6 years (1990–1996), captive subpopulations diverged significantly from the natural population. Also during this 6-year period, body lengths of captive isopods diverged nearly 2-fold from the natural population, evidently because cannibalism and thus selection favoring large size was more intense in captive subpopulations than in nature. This hypothesis is supported by the fact that cannibalism and the apparent response to selection on body size became variable among captive subpopulations when physical structure was added to three of the four SIPF pools in April 1997. As expected if cannibalism was the source of selection for large body size, by August 1998 (15 months = 7–8 generations), the rate at which body size increased became inversely proportional to the amount of physical structure within pools. Although we are unable to separate the specific effects of population subdivision and cannibalism, our results show that these conditions in combination caused rapid changes in genetic variation and the external morphology of these captive subpopulations. Our results have important implications for future attempts to manage and propagate endangered species.     

Effects of temperature on the development and survival of an endangered butterfly,Lycaeides argyrognomon (Lepidoptera: Lycaenidae) with estimation of optimal and threshold temperatures using linear and nonlinear models

The effects of temperature on the development and survival of Lycaeides argyrognomon were examined in the laboratory. The eggs, larvae and pupae were reared at temperatures of 15, 17.5, 20, 25, 30 and 33°C under a long‐day photoperiod of 16‐h light and 8‐h darkness. The survival rates of the first–third instars ranged from 40.0 to 82.4%. The mortalities of the fourth instar were lower than those of the first–third instars. The development time of the overall immature stage decreased from 78.33 days at 15°C to 21.07 days at 30°C, and then increased to 24.33 days at 33°C. The common linear model and the Ikemoto–Takai model were used to estimate the thermal constant (K) and the developmental zero (T₀). The values of T₀ and K for the overall immature stages were 10.50°C and 418.83 degree‐days, and 9.71°C and 451.68 degree‐days by the common model and the Ikemoto–Takai model, respectively. The upper temperature thresholds (T_max) and the optimal temperatures (T_opt) of the egg, the first–third instars and the overall immature stages were estimated by the three nonlinear models. The ranges of T_opt estimated were from 30.33°C to 32.46°C in the overall immature stages and the estimates of T_max of the overall immature stages by the Briere‐1 and the Briere‐2 models were 37.18°C and 33.00°C, respectively. The method to predict the developmental period of L. argyrognomon using the nonlinear models was discussed based on the data of the average temperature per hour.