Thesis (M.Sc. (Zoology & Entomology)) - Rhodes University, 2008.

Inbreeding is associated with reduced fitness, a phenomenon known as inbreeding depression. I investigated direct and indirect effects of inbreeding on social traits associated with parental care in the burying beetle, Nicrophorus vespilloides. This species breeds on small vertebrate carcasses and the parents provide care by maintaining the carcass and regurgitating food to begging larvae. I quantified the survival of outbred offspring produced by inbred and outbred parents. I found that inbred offspring had reduced survival compared to outbred offspring, and that outbred offspring produced by inbred parents survived less well. Such intergenerational effects of inbreeding suggests that inbreeding may affect the amount of parental care provided to offspring. I tested this by investigating the amount of care inbred and outbred male and female parents provided to outbred offspring. I found no reductions in the amount of care provided by inbred parents but found that parents provided more care when their partner was inbred. In addition, I investigated effects of inbreeding on parent-offspring communication, when either female parents or their offspring were inbred. I found that whilst inbred offspring begged less, parents provided inbred offspring with more care. The effects of inbreeding had significant consequences affecting biparental negotiation and parent-offspring communication. Next, I tested for the effects of inbreeding on the antimicrobial properties of secretions that both parents apply to the carcass during larval development. I found that the bactericidal activity of inbred male parents was reduced compared to outbred male parents during the dispersal stages and no evidence for the secretions of inbred and outbred female parents differing. Finally, to test whether the strong inbreeding depression found in this species influenced the mating decisions, I presented females with related or unrelated males, and found no evidence that females avoided inbreeding. These results show that to accurately estimate the fitness consequences of inbreeding the social effects on all individuals within a family must be accounted for.

The cost of reproduction hypothesis suggests that allocation into current reproduction constrains future reproduction. How organisms accrue reproductive costs may differ between species and with varying levels of resource quality. Burying beetles are model organisms for testing for the cost of reproduction because of their unique natural history; beetles utilize small vertebrate carcasses for reproduction and they and their offspring feed exclusively on these discrete resources. Burying beetles also can utilize a large range of carcass sizes for reproduction. We tested for the cost of reproduction in two species of burying beetles, Nicrophorus marginatus and Nicrophorus guttula found in Central Utah by breeding beetles on a range of carcass sizes (5g, 10g, 20g, 30g, 40g, and 50g carcasses). We also used a manipulation experiment to force beetles into over-allocating energy into reproduction to assess reproductive costs. For both species, reproduction was costly, with beetles suffering reduced lifespan and reduced lifetime fecundity with increased resource quality. Both species also showed clear signs of senescence, having reduced brood size and lower efficiency as individuals aged. Females did not show indications of terminal investment in terms of female mass change, unlike the previously studied Nicrophorus orbicollis, which gained less mass after each reproductive attempt as it aged. Nicrophorus marginatus consistently outperformed N. guttula in terms of total number of offspring produced for all carcass sizes. Nicrophorus guttula populations may continue to persist with N. marginatus by exploiting a less desirable but more abundant resource.

The forensic application of entomology is well known, but it is generally a field which concentrates on Diptera. Many Coleoptera also have forensic application, but are generally neglected by forensic entomology researchers. Necrophilic Coleoptera are diverse and therefore have application in estimating Post-Mortem Interval (PMI) by community composition, but they are also valuable in estimating PMI by development. In addition, Coleoptera are more common in stored product cases. Six species of forensically important Coleoptera were studied, three from the family Dermestidae (Dermestes haemorrhoidalis, D. maculatus and D. peruvianus) and three from the family Silphidae (Silpha punctulata, Thanatophilus micans and T. mutilatus). The effect of killing method and storage time on larval length was investigated in T. micans. Coleopteran larvae were shown not to behave in the same way as dipteran larvae. In contrast to dipteran larvae, it is recommended that coleopteran larvae be killed using ethanol. A development model is presented for T. micans. This represents the first statistically robust development model for forensically important Coleoptera, and the first development model for forensically important Silphidae. The model offers a method of estimating PMI which can be used once Diptera are no longer present on a corpse. Upper lethal temperature limits for four species of carcass beetle were determined. A comparison between species shows distinct differentiation between families and species. This differentiation accounts for microhabitat differences which these species show on carcasses. Bioclimatic models for the six species showed contrasting distributions, with both widespread and localised species. These models allow forensic investigators to assess whether the absence of a species from a corpse is forensically significant, or a result of the species distributions. Moisture-related variables were shown to be more important in predicting species distributions than temperature at a regional scale. Forensic entomology standards can be adjusted based on the findings of this study. Length was again shown to be an inferior measurement of larval age. Coleopteran development has been shown to be useful, and should be given greater consideration in future work. T. micans has been shown to be capable of locating and ovipositing on carcasses promptly after death, making it a good forensic indicator. Further work is needed for the full potential of necrophilic Coleoptera to be realised.

Sexual conflict arises in biparental species because of the fitness payoffs of shifting the costs of care onto their partner. The negotiation model asserts that parents actively monitor their partner’s level of investment and adjust their own in response generally resulting in partial compensation when a member of the pair reduces their level of investment. The willingness of one parent to compensate for the other’s change is found to be widely variable. Habitat or resource quality available to pairs may explain such variation. It is predicted that the level of compensation by one partner will increase with decreasing resource quality. I tested this prediction with the biparental burying beetle, <i>Nicrophorus orbicollis</i>. Under natural conditions, burying beetles apply costly social immune molecules to carcasses of small vertebrates to preserve nutritional value for young. The goals of this research were (1) to determine if males immunologically compensate when females are immunologically handicapped; and (2) determine the impact of resource quality on compensation. Changes in lysozyme-like-activity (LLA) and phenoloxidase (PO) production in oral and anal secretions were used to quantify social immune investment. Pairs were provided a mouse carcass of one of three qualities: freshly thawed, aged for 3 days, or aged for 7 days. As expected, female LLA decreased once injected with lipopolysaccharide (LPS) irrespective of carcass quality. Injections caused significant down regulation of oral PO in females. Male LLA increased as the quality of carcasses decreased when paired with handicapped females. Males showed no changes in PO across treatments or carcass types. My results demonstrate that males compensate for a change in maternal investment and the level of compensation increases as resource quality decreases.

Many animal species invest in extended parental care for their offspring. Parental care is costly, and natural selection favors investment strategies which maximize reproductive success. Biparental care is relatively rare, but when it does occur it has been found to increase success in terms of offspring survival and growth and in terms of future reproductive opportunities. In burying beetles (<i>Nicrophorus</i> spp.), both male and female participate in extended parental care. However, the fitness benefits of biparental care in burying beetles have been difficult to establish, with some studies reporting significantly smaller broods produced when both male and female are present. Variation in environmental conditions, such as temperature, is an important part of the context in which biparental care evolves. I hypothesize that biparental care acts as a buffer against environmental variation. This hypothesis predicts that biparental care will lead to greater reproductive success compared to uniparental care when temperature is increased during a reproductive attempt. I also tested the load-lightening hypothesis, which holds that biparental care benefits future reproduction by lowering the costs of reproduction. This predicts that the additional care by the other parent will allow females to rear higher quality second broods. I conducted a male removal experiment at two temperature treatments, using the species <i>Nicrophorus orbicollis</i>. I measured reproductive success during manipulated first brood and during second broods which females reared without a male, regardless of prior experience. I found that, contrary to my hypothesis, biparental care at the higher temperature resulted in reduced reproductive success compared to uniparental care. I found no effect of biparental care on the success of second broods. Instead, I found evidence of reproductive restraint associated with the higher temperature treatment in delayed egg-laying and increased feeding during second broods.

<div>Animal species that consume carrion provide an essential ecosystem service by recycling the resource’s nutrients intothe ecosystem. Carrion is an unpredictable and ephemeral resource that is variable across a landscape and is an important resource to many taxa. Furthermore, the colonization of small vertebrate carcasses by different species influences competition and coexistence dynamics, which in turn influence species dominance. The American burying beetle, <i>Nicrophorus americanus</i>(ABB) has recently experienced a dramatic decline in abundance and geographic range. An essential requirement of the ABBs life cycle is the availability of small vertebrate carcasses for reproduction. We know little about the preferred carrion base necessary to support a healthy ABB population. However, we know that reproduction is costly in buying beetles, and physiological trade-offs associated with resource use likely influences metabolic activity, fecundity, and survivorship. Furthermore, successful monitoring of wildlife populations requires reliable estimates of abundance, dispersal, and population demographics. This is often problematic within ABB populations because they are elusive, nocturnal, often occur at low population densities, and are a species of conservation concern. These factors constitute a management and conservation challenge in ecology and conservation biology. Therefore, identifying and evaluating the resources used for reproduction, along with life history trade-offs associated with resource use, in addition to species abundance within a habitat are key requirements for this species’ conservation and management. We used stable isotope analysis of carbon and nitrogen to determine the carrion base used by burying beetles in situ. Additionally, we evaluated resting metabolic rate and the energetics of prehatching parental care using flow through respirometry. Finally, we investigated the utility of using photographs with an individual identification machine learning software program paired with program MARK to estimate population abundances of burying beetles.<br></div><div><br></div><div>Between populations, ABBs are not specializing on either avian or mammalian carrion but are using both natural and provisioned carrion for reproduction. Furthermore, among co-occurring burying beetle species, we observed large niche overlap in both populations. Periods of sexual development and prehatching parental care were periods of elevated metabolic activity, which provides insight into life-history tradeoffs associated with resource quality. Carcass size did not significantly influence the metabolic rate of parents, however, the number of days needed to 13prepare a small carcass was significantly shorter compared to large carcass preservation. Furthermore, beetle pairs on larger carcasses accumulated significantly larger metabolic cost over the course of parental care. Additionally, using digital images of naturally occurring spot patterns on beetles’ elytra, we tested the feasibility and the application of photographic mark-recapture (PMR) using machine learning software. We demonstrated the utility of using PMR in estimating population abundance for Nicrophorusspp. based on elytral spot patterns. Future research is needed to fully quantify reproductive resource use over time, and how it influences ABB abundance in extant and reintroduced populations. For successful management and reintroduction of ABBs, managers must consider the resources used for reproduction, the composition and availability of appropriately sized potential reproductive carrion, they should limit intra-/interspecific competition for carrion resources and need accurate data on species abundance.<br></div><div><br></div><div><br></div>

In this thesis I investigated the genetic basis of several behaviours to answer questions surrounding the evolution and mechanistic basis of behaviour. Firstly, I took a single-gene approach to investigate the influence of fruitless (fru) on the courtship behaviour of Drosophila. fru is an alternatively-spliced transcription factor that is necessary for the production of male sexual behaviours, and has also been implicated in producing species-specific differences in courtship song. I investigated the patterns of selection acting on fru at the sequence level and found that positive selection was restricted to the alternatively spliced exons of fru. From this I hypothesised that the positively selected changes in fru would contribute to species-specific differences in courtship song. To test this I examined how isoform-specific fru loss-of-function mutants influence courtship song, and generated “species-swapped” flies whereby regions of fru that showed evidence for positive selection were transferred from four species of Drosophila, into D. melanogaster. Contrary to prediction, I found flies that lacked isoforms containing positively selected regions did not show any differences in courtship song. Unfortunately “species-swapped” flies were not generated in time to examine phenotypes and neuroanatomy as intended. Next, I examined the genetic basis of cold acclimation in two species of Drosophila using a transcriptomic approach. I found that the genes differentially expressed in response to cold acclimation were largely different in each of the species; however, the biological processes they were involved in were broadly similar. Finally, I investigated the transcriptomic changes associated with parental care in the burying beetle Nicrophorus vespilloides to determine if males and females alter the genes they express when parenting alone versus with a partner. I found that males greatly reduced their transcriptional response when parenting with a partner, suggesting they reduce the care they provide when present with a female.