Induction of ovarian growth in the red claw crayfish,Cherax quadricarinatus,by the enkephalinergic antagonist naloxone: in vivo and in vitro studies

Summary

The effects of spiperone and domperidone (dopaminergic antagonists), as well as naloxone (enkephalinergic antagonist) on ovarian growth of the crayfish Cherax quadricarinatus, were evaluated during the non-reproductive period. In vivo assays were carried out by administering these compounds by adding them to the crayfish food, and subsequently measuring the oocyte diameter (oocytes in secondary vitellogenesis). Only naloxone produced a significantly (p <0.05) higher oocyte diameter than that of the controls, suggesting that this antagonist was blocking the effects of endogenous enkcephalins on the secretion of one or more neurohormones involved in crustacean reproduction. To test this hypothesis, an in vitro incubation of ovarian pieces with thoracic ganglion (TG), a source of the gonad stimulating hormone (GSH), or eyestalk tissue (ET), the source of the gonad inhibiting hormone (GIH), with or without naloxone added to the incubation medium, was done. A significant increase of ovarian growth was observed when TG was present. Moreover, the addition of naloxone to this preparation was able to further increase the ovarian growth, presumably by preventing enkephalinergic inhibition of GSH secretion.     

External factors determining seasonal breeding in a subtropical population of the shore crab Pachygrapsus transversus (Gibbes, 1850) (Brachyura,Grapsidae)

Summary

Monthly samples of the shore crab Pachygrapsus transversus from two distinct annual periods showed that ovigerous females are present throughout the year in the population. However, the relative ovigerous abundance of specimens among sexually mature changes from less than 10% during the winter months to almost 80% in summer. Linear correlations for each year revealed that both temperature and photoperiod were positively associated with relative abundance of ovigerous females. Multiple regression analyses suggested that photoperiod was the main factor affecting breeding in this species. Timing of observed reproductive pattern may enhance larval survival because of particular oceanographic conditions in the study region and favor early juvenile development due to certain species-specific growth features.     

Interspecific Infanticide and Infant‐Directed Aggression by Spider Monkeys (Ateles hybridus) in a Fragmented Forest in Colombia

Interspecific aggression amongst nonhuman primates is rarely observed and has been mostly related to scenarios of resource competition. Interspecific infanticide is even rarer, and both the ultimate and proximate socio‐ecological factors explaining this behavior are still unclear. We report two cases of interspecific infanticide and five cases of interspecific infant‐directed aggression occurring in a well‐habituated primate community living in a fragmented landscape in Colombia. All cases were initiated by male brown spider monkeys (Ateles hybridus) and were directed toward infants of either red howler monkeys (Alouatta seniculus: n = 6 cases) or white‐fronted capuchins (Cebus albifrons: n = 1 case). One individual, a subadult spider monkey male, was involved in all but one case of interspecific infanticide or aggression. Other adult spider monkeys participated in interspecific aggression that did not escalate into potentially lethal encounters. We suggest that competition for food resources and space in a primate community living in high population densities and restricted to a forest fragment of ca. 65 ha might partly be driving the observed patterns of interspecific aggression. On the other hand, the fact that all but one case of interspecific infanticide and aggression involved the only subadult male spider monkey suggests this behavior might either be pathological or constitute a particular case of redirected aggression. Even if the underlying principles behind interspecific aggression and infanticide are poorly understood, they represent an important factor influencing the demographic trends of the primate community at this study site. Am. J. Primatol. 74:990‐997, 2012. © 2012 Wiley Periodicals, Inc.     

Host preference of a temperate mistletoe: Disproportional infection on three co‐occurring host species influenced by differential success

The mistletoe Tristerix verticillatus (Loranthaceae) parasitizes within a small area of the Yerba Loca Nature Sanctuary near Santiago, Chile, three co‐occurring hosts: Schinus montanus (Anacardiaceae), Fabiana imbricata (Solanaceae) and Berberis montana (Berberidaceae). Previous studies suggest that T. verticillatus may be favoured when parasitizing S. montanus relative to the other two host species. We hypothesize that infection of S. montanus is not proportional to its local abundance or appearance, that S. montanus is more intensively parasitized than other available hosts, and that host provenance is a determinant of the fate of the infecting seed. We compare the incidence of infection of T. verticillatus in relation to local availability and appearance variables, and the intensity of infection of T. verticillatus, on the three co‐occurring host species. We then test the effects of host provenance on mistletoe seed establishment success with a seed cross inoculation experiment varying the donor and receptor hosts. Finally, we test whether there are differences in establishment success between manually processed seeds and seeds defecated by the avian disperser Mimus thenca (Passeriformes: Mimidae). Our results show that the three hosts have an aggregated spatial distribution. Schinus montanus was parasitized at a higher rate than expected by its local availability and appearance, and inoculated seeds showed differential development depending on the origin of the seeds: seeds from T. verticillatus parasitizing S. montanus inoculated to S. montanus twigs showed higher germination and lower mortality than seeds from T. verticillatus parasitizing F. imbricata inoculated to S. montanus twigs. Furthermore, seeds defecated by the avian disperser, M. thenca, had higher adherence and reduced mortality when compared to manually processed seeds. The disproportional host infection found is discussed in terms of the differential establishment of mistletoe seeds, morphological characteristics of hosts and the behaviour of dispersing birds.     

Phytoplankton distribution along trophic gradients within and among reservoirs in Catalonia (Spain)

1. Longitudinal gradients in the epilimnetic waters of stratified reservoirs provide a useful database to study changing environmental conditions. The spatial distribution, assemblage structure and specific adaptations of phytoplankton assemblages can be analysed along these gradients over short time scales. 2. Four reservoirs with a similar typology, located along an altitudinal gradient in the same eco‐region, were sampled along their longitudinal axes. In total, 19 sampling stations provided a trophic spectrum, ranging from oligo‐mesotrophy to hypertrophy, which was quantified by calculating the trophic state index of each sampling station in the four reservoirs. 3. Several patterns in phytoplankton assemblage structure were detected. Total chlorophyll‐a (Chl‐a), biovolume, abundance and the relative biomass contribution of the main algal groups (chlorophytes, cyanobacteria, cryptophytes and diatoms) were highly correlated with their location along the trophic gradient. 4. We also adopted the functional classification of Reynolds et al. (2002) : this effectively summarized differences among phytoplankton assemblages under varying resource‐limiting combinations, especially nutrients and underwater light climate. 5. In terms of relationships with the trophic gradient, diatoms and cyanobacteria exhibited significant opposing trends in both their relative chlorophyll contribution to total Chl‐a and biovolume. Chlorophytes were more abundant at an intermediate position along the trophic spectrum. 6. The identified patterns are consistent with models of self‐organization of phytoplankton assemblages. In particular, light availability was a strong determinant of size and shape diversity, especially in hypertrophic conditions, where ‘R‐strategist’, needle shaped species, dominated the system. In contrast, under decreased availability of nutrients and higher light extinction coefficients (K_d), the system was co‐dominated by C‐ and S‐strategist species, having shapes with a higher surface/volume ratio.     

Lolium multiflorum density responses under ozone and herbicide stress

Adaptations to overcrowding of individual plants result in density dependant control of growth and development. There is little information on how anthropogenic stresses modify these responses. We investigated whether combinations of diclofop‐methyl herbicide and tropospheric ozone alter the pattern of expected growth compensation with density changes resulting from intraspecific competition in Lolium multiforum Lam (Poacea) plants. Individual plant vegetative parameters and total seed production were assessed for plants growing under various densities and different herbicide rates and ozone treatments. The stressors differently changed the frequency distribution for average individual plant weight resulting from increasing densities. Only herbicide affected seedling mortality. Plants were able to compensate during grain filling maintaining similar seed production – density relationships in all treatments. Our findings contribute to the understanding of the impact of stress factors on the demographic changes in plant populations. Important ecological implications arise: (i) contrasting responses to ozone and herbicide, alone and in combination of individual plants resulted in different biomass – density relationships; (ii) stress effects on plant populations could not be predicted from individual responses; and (iii) changes in competitive outcome by single or combined stress factors may alter the expected genotype frequency in a crowded population with few dominant individuals.