Maternal effects on offspring size in a natural population of the viviparous tsetse fly

1. Theory predicts that mothers should adaptively adjust reproductive investment depending on current reserves and future reproductive opportunities. Females in better intrinsic state, or with more resources, should invest more in current reproduction than those with fewer resources. Across the lifespan, investment may increase as future reproductive opportunities decline, yet may also decline with reductions in intrinsic state. 2. Across many species, larger mothers produce larger offspring, but there is no theoretical consensus on why this is so. This pattern may be driven by variation in maternal state such as nutrition, yet few studies measure both size and nutritional state or attempt to tease apart confounding effects of size and age. 3. Viviparous tsetse flies (Glossina species) offer an excellent system to explore patterns of reproductive investment: females produce large, single offspring sequentially over the course of their relatively long life. Thus, per‐brood reproductive effort can be quantified by offspring size. 4. While most tsetse reproduction research has been conducted on laboratory colonies, maternal investment was investigated in this study using a unique field method where mothers were collected as they deposited larvae, allowing simultaneous mother‐offspring measurements under natural conditions. 5. It was found that larger mothers and those with a higher fat content produced larger offspring, and there was a trend for older mothers to produce slightly larger offspring. 6. The present results highlight the importance of measuring maternal nutritional state, rather than size alone, when considering maternal investment in offspring. Implications for understanding vector population dynamics are also discussed.     

Blow fly Lucilia sericata nuclease digests DNA associated with wound slough/eschar and with Pseudomonas aeruginosa biofilm

In chronic wounds, it may be clinically important to remove extracellular bacterial and patient DNA as its presence may impede wound healing and promote bacterial survival in biofilm, in which extracellular DNA forms part of the biofilm architecture. As medicinal maggots, larvae of Lucilia sericata Meigen (Diptera: Calliphoridae) have been shown to efficiently debride wounds it became of interest to investigate their excretions/secretions (ES) for the presence of a deoxyribonuclease (DNAse) activity. Excretions/secretions products were shown to contain a DNAse, with magnesium, sodium and calcium metal ion dependency, and a native molecular mass following affinity purification of approximately 45 kDa. The affinity purified DNAse degraded genomic bacterial DNA per se, DNA from the slough/eschar of a venous leg ulcer, and extracellular bacterial DNA in biofilms pre‐formed from a clinical isolate of Pseudomonas aeruginosa. The latter finding highlights an important attribute of the DNAse, given the frequency of P. aeruginosa infection in non‐healing wounds and the fact that P. aeruginosa virulence factors can be toxic to maggots. Maggot DNAse is thus a competent enzyme derived from a rational source, with the potential to assist in clinical wound debridement by removing extracellular DNA from tissue and biofilm, and promoting tissue viability, while liberating proteinaceous slough/eschar for debridement by the suite of proteinases secreted by L. sericata.     

Effects of river temperature and climate warming on stock‐specific survival of adult migrating Fraser River sockeye salmon (Oncorhynchus nerka)

Mean summer water temperatures in the Fraser River (British Columbia, Canada) have increased by ～1.5 °C since the 1950s. In recent years, record high river temperatures during spawning migrations of Fraser River sockeye salmon (Oncorhynchus nerka) have been associated with high mortality events, raising concerns about long‐term viability of the numerous natal stocks faced with climate warming. In this study, the effect of freshwater thermal experience on spawning migration survival was estimated by fitting capture–recapture models to telemetry data collected for 1474 adults (captured in either the ocean or river between 2002 and 2007) from four Fraser River sockeye salmon stock‐aggregates (Chilko, Quesnel, Stellako‐Late Stuart and Adams). Survival of Adams sockeye salmon was the most impacted by warm temperatures encountered in the lower river, followed by that of Stellako‐Late Stuart and Quesnel. In contrast, survival of Chilko fish was insensitive to the encountered river temperature. In all stocks, in‐river survival of ocean‐captured sockeye salmon was higher than that of river‐captured fish and, generally, the difference was more pronounced under warm temperatures. The survival–temperature relationships for ocean‐captured fish were used to predict historic (1961–1990) and future (2010–2099) survival under simulated lower river thermal experiences for the Quesnel, Stellako‐Late Stuart and Adams stocks. A decrease of 9–16% in survival of all these stocks was predicted by the end of the century if the Fraser River continues to warm as expected. However, the decrease in future survival of Adams sockeye salmon would occur only if fish continue to enter the river abnormally early, towards warmer periods of the summer, as they have done since 1995. The survival estimates and predictions presented here are likely optimistic and emphasize the need to consider stock‐specific responses to temperature and climate warming into fisheries management and conservation strategies.     

Foraging site recursion by forest elephants Elephas maximus borneensis

Recursion by herbivores is the repeated use of the same site or plants. Recursion by wild animals is rarely investigated but may be ubiquitous. Optimal foraging theory predicts site recursion as a function of the quality of the site, extent of its last use, and time since its last use because these influence site resource status and recovery. We used GPS collars, behaviour and site sampling to investigate recursion to foraging sites for two elephant Elephas maximus borneensis herds in the Lower Kinabatangan Wildlife Sanctuary, Borneo, over a 12 month period. Recursion occurred to 48 out of 87 foraging sites and was most common within 48 hours or between 151-250 days, indicating two different types ofrecursion. Recursion was more likely to occur if the site had previously been occupied for longer. Moreover, the time spent at a site at recursion was the same as the time spent at the site on the first occasion. The number of days that had passed between the first visit and recursion was also positively correlated with how much time was spent at the site at recursion. Habitat type also influenced the intensity of site-use, with more time spent at recursion within riverine/open grass areas along forest margins compared to other habitat types. Recursion is a common behaviour used by the elephants and its pattern suggests it may be a foraging strategy for revisiting areas of greater value. The qualities of recursion sites might usefully be incorporated into landscape management strategies for elephant conservation in the area [Current Zoology 60 （4）： 551-559, 2014].     

Evaluation of the population dynamics of the forage legume (Lotus corniculatus), using matrix population models

The population dynamics of perennial crop plants are influenced by numerous factors, including management practices. Conditions in the field vary from year to year, and matrix population models are useful for evaluating population behaviour in relation to environmental variability. In Missouri, the stand persistence of birdsfoot trefoil ( Lotus corniculatus ), a perennial legume, is often limited by disease and poor seed production. A stage-based, matrix population model was developed to evaluate the population dynamics of birdsfoot trefoil in relation to clipping treatment. The plant growth stages represented in the model were seeds, seedlings, mature vegetative and reproductive plants. Two phases of population growth were evaluated in clipped and unclipped stands. Establishment-phase populations were characterized by relatively high mortality and low reproduction. Elasticity analysis indicated that growth of these populations was most sensitive to the survival of vegetative plants. Mature vegetative plants and seeds comprised the majority of surviving individuals in clipped and unclipped populations, respectively; however, establishment-phase populations under both management treatments tended toward extinction. Populations in the post-establishment phase of growth were characterized by relatively low mortality and high reproduction. Population growth in this phase of growth was most sensitive to seed production, and most individuals in these populations were at the seed stage.     

Interlimb Coordination During Locomotion

SYNOPSIS. Studies of interlimb control during cat locomotionare directed at four different levels of organization. Interlimbstepping patterns are described from studies of the timing ofelectromyographic activity of muscles of different limbs. Patternsof coordination are based on the frequency of occurrence ofthe phasing of step cycles of the different limbs. Selectivespinal cord lesions are used to perturb those patterns of coordinationand have implicated two ascending spinal systems in interlimbcontrol: long ascending propriospinal neurons (LAPNs) and neuronsof the ventral spinocerebellar tract (VSCT). The results ofneuroanatomical tract tracing experiments indicate that twodifferent populations of LAPNs exist which might provide directconnection between cervical and lumbosacral locomotor centersbut that neurons of the VSCT do not make such connections. Theseresults imply that the role of the VSCT in interlimb controlis by way of the cerebellum. Unit recordings made from axonsof the VSCT during treadmill locomotion are consistent withthe VSCT carrying information about the timing of both hindlimbstep cycles.