Telomere dynamics in a lizard with morph‐specific reproductive investment and self‐maintenance

Telomeres in human fibroblasts shorten progressively during in vitro culturing and trigger replicative senescence. Furthermore, shortened telomeres can be used as biomarkers of disease. These observations have led to the suggestion that telomere dynamics may also be associated with viability and selection for life history variation in non‐human taxa. Model systems to examine this suggestion would particularly benefit from the coexistence of multiple phenotypes within the same species with different life history trade‐offs, since those could be compared in terms of telomere characteristics. This scenario also provokes the classic question of why one morph does not have marginally higher fitness and replaces the others. One explanation is that different morphs have different reproductive tactics with equal relative fitness. In Australian painted dragons (Ctenophorus pictus), males differ in head color, the presence or absence of a gular bib, and reproductive expenditure. Red males out‐compete yellow males in dominance contests, while yellow males copulate quickly and have higher success in sperm competition than red males. Males with bibs better defend partners against rival matings, at the cost of loss of body condition. We show that yellow‐headed and bib‐less males have longer telomeres than red, blue and bibbed males, suggesting that telomere length is positively associated with higher investment into self‐maintenance and less reproductive expenditure.     

Male receiver bias for red agonistic signalling in a yellow-signalling widowbird: a field experiment

Receiver bias models of signal evolution are typically regarded as alternatives or complements to ornament evolution due to coevolving mate choice, whereas sexually or socially selected agonistic signals are rarely studied with respect to receiver psychology. Against the background of convergent evolution of red agonistic signals from yellow ancestors in the genus Euplectes (widowbirds and bishops), we experimentally test the function of a yellow signal in the montane marsh widowbird (E. psammocromius), as well as a hypothesized receiver bias for redder (longer wavelength) hues. In a field experiment in southern Tanzania, males that had their yellow wing patches blackened lost their territories or lost territorial contests more often than controls or reddened males, which together with a longer wavelength hue in territory holders, indicates an agonistic signal function. Males painted a novel red hue, matching that of red-signalling congeners, retained their territories and won contests more often than controls. To our knowledge, this is the first demonstration of a receiver bias driving agonistic signal evolution. Although the sensory or cognitive origin of this bias is yet unknown, it strengthens our view that genetically constrained signal production (i.e. carotenoid metabolism), rather than differential selection, explains the carotenoid colour diversification in Euplectes.     

Cutaneous leishmaniasis in red kangaroos: isolation and characterisation of the causative organisms

This is the first report of cutaneous leishmaniasis in kangaroos where infection was acquired within Australia. The diagnosis is based on the clinical criteria used for humans, the lesion histopathology, the detection and isolation of parasites from the lesions, and the analysis of the small subunit ribosomal RNA genes using the polymerase chain reaction. Despite a clear indication that the parasites belong to the genus Leishmania, no assignation to a known Leishmania species could be made using these or other less conserved genetic loci such as the non-transcribed spacer of the mini-exon repeat. As is the case in humans, some but not all animals harbouring lesions had antibodies to the isolated parasites or to several other Leishmania species. The isolated parasites displayed two well characterised Leishmania glycoconjugates, the lipophosphoglycan and proteophosphoglycan. They were infectious for mouse macrophages in vitro and established long-term infection at 33 degrees C but not at 37 degrees C. Our findings raise the possibility of transmission to humans, which may be unrecognised and suggest the possibility that imported species of Leishmania could become endemic in Australia.     

Habitat-mediated survival of newly settled red king crab in the presence of a predatory fish: Role of habitat complexity and heterogeneity

Red king crab (RKC) (Paralithodes camtschaticus) are generally associated with structurally complex habitats during the first 2 years of benthic life. In this first experimental laboratory study with a fish predator, survival of newly settled juvenile RKC was tested in eight different habitat treatments with varying amounts and types of physical structure, open sand, gravel bottom, and habitat islands. Video observations provided insights on habitat-mediated interactions between Pacific halibut predators (Hippoglossus stenolepis) and crab prey. Survival of RKC increased with amount of physical structure and was highest in the most heterogeneous habitat and in habitats characterized by high density patches. Predator activity decreased with increasing amount of structure, and attacks on RKC were correlated with predator activity. Low survival in open sand habitat was associated with both high attack rate and high capture success (captures per attack). Lower levels of capture success did not vary among the habitats containing algae and other complex physical structures, but attack rates declined with increasing amount of structure, and encounter rate (i.e., prey detection and attack) was the primary determinant of mortality. RKC were capable of detecting predators and adjusted their behavior to avoid predation by sheltering in dense microhabitat patches. Successful stock enhancement for greatly reduced populations of RKC in the Gulf of Alaska will depend upon placing seed stock in habitats with abundant protective habitat, and high quality microhabitats may serve as well as continuous cover.     

Morph-specific diurnal variation in allatostatin immunostaining in the corpora allata of Gryllus firmus: Implications for the regulation of a morph-specific circadian rhythm for JH biosynthetic rate

Previous studies have documented a circadian cycle in juvenile hormone (JH) biosynthesis in the long-winged, flight-capable morph, but not in the short-winged flightless morph of the cricket Gryllus firmus. One rapid and reversible inhibitor of in vitro JH biosynthesis by the corpora allata (CA) in crickets is the neuropeptide Phe-Gly-Leu/Ile-amide type of allatostatins (ASTs). To investigate the possible role of allatostatin regulation of the morph-specific circadian cycle of JH production, the quantity of this type of AST in the nerves within the CA was determined by the density of anti-AST-immunostaining in confocal images using the Image J program. The density of immunostaining was inversely related to the rate of JH biosynthesis: Immunostaining in the CA was high and did not differ between morphs early in the photophase when the in vitro rate of JH biosynthesis is low and equivalent in the morphs. However, during the end of the photophase, when the rate of JH biosynthesis rises dramatically in the flight-capable morph, but not in the flightless morph, immunostaining was significantly lower in the flight-capable compared to the flightless morph. These results indicate that morph-specific differences in delivery of AST to the CA and its probable release likely regulate the morph-specific circadian pattern of JH biosynthesis. Also, the negative correlation between AST density and JH production provides evidence for predicting the periods of altered release of these rapid-acting paracine regulators of JH biosynthesis.     

Differences in penetration routes and establishment rates of four entomopathogenic nematode species into four white grub species

We compared the penetration of the entomopathogenic nematodes Steinernema scarabaei (AMK001 strain), S. glaseri (NC1 strain), Heterorhabditis zealandica (X1 strain), and H. bacteriophora (GPS11 strain) into third-instars of the scarabs Popillia japonica, Anomala orientalis, Cyclocephala borealis, and Rhizotrogus majalis. When larvae were exposed to nematodes for 6-72 h larval mortality and nematode establishment rate and occasionally speed of kill often showed the same pattern within nematode-white grub combinations. But no two nematodes or white grub species had the same pattern for these observations for all white grub or nematode species, respectively. Mortality, establishment, and speed of kill followed a similar pattern for H. zealandica, S. glaseri, and S. scarabaei, but there was no clear relationship for H. bacteriophora. Significant nematode establishment was only observed after at least 48 h exposure in most nematode-white grub combinations. Faster establishment was observed only for H. zealandica in A. orientalis and R. majalis (after 24 h) and for S. scarabaei in P. japonica and R. majalis (after 12 h). Nematode establishment after 72 h in the different scarab species was generally low for S. glaseri (<1.5%) and H. bacteriophora (<3%), higher for H. zealandica (2-5%), and the highest for S. scarabaei (1-14%). However, in another experiment establishment was generally higher after 96h exposure. Nematode penetration sites were determined by comparing nematode establishment in larvae with mouth, anus, mouth+anus, or none sealed with glue. The trends for each nematode species were very similar in the different white grub species. H. zealandica and H. bacteriophora showed excellent cuticular penetration ability but may also penetrate through mouth and/or anus. S. glaseri also penetrated through the cuticle but lower establishment in larvae with mouth or mouth+anus sealed suggested that the mouth is an important penetration site. S. scarabaei showed a preference for the mouth as a penetration site, but it showed some cuticular penetration ability and may also use the anus as a penetration site. The methodology used cannot exclude that cuticular penetration also included penetration through the spiracles. To fully understand the effect of nematode and white grub species on nematode virulence, future studies will have to compare host immune response to the penetrating IJs and the role of the symbiotic bacteria in these interactions.     

Offspring size-number trade-off in a lizard with small clutch sizes: tests of invariants and potential implications

Models of small clutch sizes predict a number of invariant relationships between means and variances of measures of reproductive investment. However, empirical tests of the models have been lagging behind theoretical work. We tested the predictions using data on the mallee dragon, Ctenophorus fordi, a species where the basic assumptions of the models are likely to be fulfilled. Some, but not all, qualitative predictions of the models were shown to hold true, but the data fitted poorly to quantitative predictions. The patterns of deviation from theory may suggest the presence of a lower, and potentially an upper, limit on egg mass. We also argue that multiple and non-independent allocation decisions between total reproductive effort, growth and maintenance, and offspring size-number allocation could be important factors in the evolution of size-number strategies in lizards and thus need to be taken into account in theoretical models. The present study shows the potential to use small clutch size models to gain further insights into reproductive investment and allocation decisions in squamates.     

High survival and growth rates of introduced Pacific oysters may cause restrictions on habitat use by native mussels in the Wadden Sea

Pacific oysters Crassostrea gigas (Thunberg, 1793) were introduced to the northern Wadden Sea (North Sea, Germany) by aquaculture in 1986 and finally became established. Even though at first recruitment success was rare, three consecutive warm summers led to a massive increase in oyster abundances and to the overgrowth of native mussel beds (Mytilus edulis L.). These mussels constitute biogenic reefs on the sand and mud flats in this area. Survival and growth of the invading C. gigas were investigated and compared with the native mussels in order to predict the further development of the oyster population and the scope for coexistence of both species. Field experiments revealed high survival of juvenile C. gigas (approximately 70%) during the first three months after settlement. Survival during the first winter varied between > 90% during a mild and 25% during a cold winter and was independent of substrate (i.e., mussels or oysters) and tide level. Within their first year C. gigas reached a mean length of 35-53 mm, and within two years they grew to 68-82 mm, which is about twice the size native mussels would attain during that time. Growth of juvenile oysters was not affected by substrate (i.e., sand, mussels, and other oysters), barnacle epibionts and tide level, but was facilitated by fucoid algae. By contrast, growth of juvenile mussels was significantly higher on sand flats than on mussel or oyster beds and higher in the subtidal compared to intertidal locations. Cover with fucoid algae increased mussel growth but decreased their condition expressed as dry flesh weight versus shell weight. High survival and growth rates may compensate for years with low recruitment, and may therefore allow a fast population increase. This may lead to restrictions on habitat use by native mussels in the Wadden Sea.