Introduced species cause both considerable ecological and economic damage every year. However, not much is known about how certain species are able to establish and spread beyond the site of initial introduction, whereas others do not. Species undergoing range expansion following an introduction may prove to be a valuable resource to invasion biology, but may also be informative in light of species' responses to changing environments (i.e. global climate change). Here, I took advantage of an ongoing range expansion of an introduced vertebrate species. House sparrows (Passer domesticus) were introduced to Mombasa, Kenya in the 1950s and have subsequently expanded their range northwest-ward and now occupy most major cities in Kenya. By comparing older, established populations (i.e. those in Mombasa) with more recently colonized populations at the range edge, it might be possible to determine some of the mechanisms that underlie range expansion in some species and/or populations. In Chapter 1, the background and ideas that motivated the rest of the dissertation is summarized. In Chapter 2, I studied how exploration and glucocorticoids (a hormone released in response to stressors) changed throughout the range expansion. Exploration was greater at the range edge, which is likely to ensure greater discovery of novel resources. Glucocorticoids released in response to restraint were also highest at the range edge, which might facilitate resolution of stressors in unpredictable environments. However, chronically elevated levels of glucocorticoids are often considered maladaptive, unless an individual can appropriately cope with them. Therefore, in Chapter 3, I characterized glucocorticoid receptors (i.e. mineralocorticoid receptor (MR) and glucocorticoid receptor (GR)) in the hippocampus, an area responsible for negative feedback of glucocorticoids as well as induction of behavioral and physiological response to stressors. I found that MR density was lower relative to GR density at the range edge compared to the site of introduction (Mombasa). I speculate this pattern is a mechanism to resolve the elevated levels of glucocorticoids at the range edge. Taken together, these results indicate that individuals at the range edge have a strong glucocorticoid response to stressors to induce a rapid, strong response to resolve stressors. Subsequently, in Chapter 4, I examined the potential mechanisms of phenotypic change among Kenyan house sparrows. Typically, following an introduction event, genetic diversity undergoes a bottleneck and is greatly reduced compared to the source population; as such, genetic evolution as the main driver of changing phenotypes throughout the range expansion is unlikely. We therefore hypothesized that epigenetic mechanisms (e.g. DNA methylation) may compensate for the expected reduced genetic diversity following an introduction. Although there was no pattern of epigenetic variation among cities (i.e. variation did not increase nor decrease further from the site of introduction), epigenetic variation increased as genetic inbreeding increased (a sign of reduced genetic diversity and bottlenecks), suggesting epigenetic modifications may compensate for reduced genetic diversity following an introduction event. Overall, patterns of phenotypic variation emerged dependent on age of the population- these patterns may prove to be important in other vertebrate range expansions as well. Surprisingly, epigenetic diversity did not correlate with phenotypic variation among populations; however, within-individual studies may reveal epigenotypes are related to certain behavioral or physiological phenotypes. In the future, studies should be designed to address how phenotypic differences arise despite relatively low genetic diversity and overall high genetic admixture among individuals. In Kenyan house sparrows, maintenance of high levels of flexibility and differential developmental influences may be important factors that lead to varying phenotypes dependent on time since colonization.

O Brasil é um dos países com a maior riqueza de aves do mundo (1.677 espécies). A Ordem Passeriformes detém 56% desta riqueza, incluindo o sabiálaranjeira Turdus rufiventris e o pardal Passer domesticus (introduzido), espécies cuja composição, padrão e estrutura da comunidade de helmintos foram investigadas nesta pesquisa. As aves (N=160 de cada espécie) foram capturadas com o auxílio de alçapões e de redes de neblina em paisagens urbanas e rurais da Região Metropolitana de Porto Alegre, RS. Quinze espécies de helmintos foram encontradas no sabiá-laranjeira (sete nematóides, quatro digenéticos, três cestóides e um acantocéfalo), com riqueza média de 2,92 espécies/hospedeiro. No pardal, a riqueza média foi de 0,19 espécies/hospedeiro e cinco espécies de helmintos foram encontradas (dois digenéticos, dois nematóides e um cestóide). Nove espécies foram dominantes, cinco co-dominantes e uma subordinada na comunidade de helmintos do sabiá, enquanto para o pardal, quatro espécies foram dominantes e uma co-dominante. Machos e fêmeas adultos das duas espécies hospedeiras apresentaram comunidades de parasitos semelhantes. Os sabiás-laranjeira adultos, por sua vez, tiveram uma maior riqueza de parasitos do que os juvenis. A fauna parasitária encontrada nestas espécies hospedeiras reflete em grande parte a dieta das aves, considerando que muitas das espécies de helmintos são adquiridas através da ingestão de hospedeiros intermediários infectados. As variações na prevalência apresentada por algumas espécies de helmintos entre as diferentes estações do ano e na riqueza da helmintofauna entre as paisagens rural e urbana são compatíveis com possíveis diferenças na disponibilidade de invertebrados e/ou de outros itens alimentares (tais como frutos) nestas épocas e/ou paisagens dominadas por ambientes distintos.

O Brasil é um dos países com a maior riqueza de aves do mundo (1.677 espécies). A Ordem Passeriformes detém 56% desta riqueza, incluindo o sabiálaranjeira Turdus rufiventris e o pardal Passer domesticus (introduzido), espécies cuja composição, padrão e estrutura da comunidade de helmintos foram investigadas nesta pesquisa. As aves (N=160 de cada espécie) foram capturadas com o auxílio de alçapões e de redes de neblina em paisagens urbanas e rurais da Região Metropolitana de Porto Alegre, RS. Quinze espécies de helmintos foram encontradas no sabiá-laranjeira (sete nematóides, quatro digenéticos, três cestóides e um acantocéfalo), com riqueza média de 2,92 espécies/hospedeiro. No pardal, a riqueza média foi de 0,19 espécies/hospedeiro e cinco espécies de helmintos foram encontradas (dois digenéticos, dois nematóides e um cestóide). Nove espécies foram dominantes, cinco co-dominantes e uma subordinada na comunidade de helmintos do sabiá, enquanto para o pardal, quatro espécies foram dominantes e uma co-dominante. Machos e fêmeas adultos das duas espécies hospedeiras apresentaram comunidades de parasitos semelhantes. Os sabiás-laranjeira adultos, por sua vez, tiveram uma maior riqueza de parasitos do que os juvenis. A fauna parasitária encontrada nestas espécies hospedeiras reflete em grande parte a dieta das aves, considerando que muitas das espécies de helmintos são adquiridas através da ingestão de hospedeiros intermediários infectados. As variações na prevalência apresentada por algumas espécies de helmintos entre as diferentes estações do ano e na riqueza da helmintofauna entre as paisagens rural e urbana são compatíveis com possíveis diferenças na disponibilidade de invertebrados e/ou de outros itens alimentares (tais como frutos) nestas épocas e/ou paisagens dominadas por ambientes distintos.

O Brasil é um dos países com a maior riqueza de aves do mundo (1.677 espécies). A Ordem Passeriformes detém 56% desta riqueza, incluindo o sabiálaranjeira Turdus rufiventris e o pardal Passer domesticus (introduzido), espécies cuja composição, padrão e estrutura da comunidade de helmintos foram investigadas nesta pesquisa. As aves (N=160 de cada espécie) foram capturadas com o auxílio de alçapões e de redes de neblina em paisagens urbanas e rurais da Região Metropolitana de Porto Alegre, RS. Quinze espécies de helmintos foram encontradas no sabiá-laranjeira (sete nematóides, quatro digenéticos, três cestóides e um acantocéfalo), com riqueza média de 2,92 espécies/hospedeiro. No pardal, a riqueza média foi de 0,19 espécies/hospedeiro e cinco espécies de helmintos foram encontradas (dois digenéticos, dois nematóides e um cestóide). Nove espécies foram dominantes, cinco co-dominantes e uma subordinada na comunidade de helmintos do sabiá, enquanto para o pardal, quatro espécies foram dominantes e uma co-dominante. Machos e fêmeas adultos das duas espécies hospedeiras apresentaram comunidades de parasitos semelhantes. Os sabiás-laranjeira adultos, por sua vez, tiveram uma maior riqueza de parasitos do que os juvenis. A fauna parasitária encontrada nestas espécies hospedeiras reflete em grande parte a dieta das aves, considerando que muitas das espécies de helmintos são adquiridas através da ingestão de hospedeiros intermediários infectados. As variações na prevalência apresentada por algumas espécies de helmintos entre as diferentes estações do ano e na riqueza da helmintofauna entre as paisagens rural e urbana são compatíveis com possíveis diferenças na disponibilidade de invertebrados e/ou de outros itens alimentares (tais como frutos) nestas épocas e/ou paisagens dominadas por ambientes distintos.

Badges of status are supposed to have insignificant production costs, so use costs are thought to be most important in ensuring signal reliability. Use costs arise from the use of the status signal in social interactions. Social experiences that arise from the use of inappropriate signals in social interactions may drive mechanisms that result in reduced fitness for inappropriate signalers. The role of social control, probing and familiarity in producing use costs was explored. There was no evidence that social control by dominants produced a cost for cheaters and no evidence that social control by subordinates produced a cost for inappropriate signaling by Trojans. Probing produced a cost for cheating when resource value was high but not when resource value was low. Familiarity had some effect on the cost and benefit of cheating but in patterns that were not predicted. Familiarity both eliminated a benefit of cheating and reduced a cost of cheating; therefore it is uncertain how familiarity affects honest signaling. The status signal of the receiver had no effect on the cost or benefits of cheating, and there was no evidence of punishment. Social experiences have the potential to affect signal development to produce a correspondence between signal and status. The effects of social experience on signal production were examined and there was little evidence that social experience influenced bib development. Neither aggression expressed nor aggression received was not predictive of bib size. Additionally, tests on the different measures of winning experience produced conflicting conclusions regarding the relationship between winning experience and bib development.

Introduced species are the greatest threat to biodiversity after habitat loss. Understanding the processes that permit organisms to become successful invaders may provide opportunities to prevent or limit their dispersal and establishment and thereby alleviate some of their harmful effects. The goal of my dissertation research has been to investigate whether invasive species have distinctive interactions with parasites, and some of the mechanisms that may underlie that variation. I used one of the world's most successful vertebrate invaders as a case study: the house sparrow (Passer domesticus; Introduction). Previous research in the house sparrow suggested that loss of parasite diversity may contribute to invasion success. However, my work demonstrates that infection with common avian malaria parasites is primarily a function of environmental heterogeneity and is not a predictor of time since introduction for house sparrows that are currently expanding their range in Kenya (Chapter 1). Interestingly, in spite of a large proportion of the population being infected with avian malaria, a state that should reduce competitive ability of house sparrow populations, this species is still able to establish themselves among native competitors. Though there are a number of potential mechanisms that could explain this pattern, one of the most convincing explanations is that house sparrows, and perhaps other introduced species, have adaptive differences in immunity. As such, the findings of Chapter 1 inspired two studies in which my collaborators and I showed that house sparrows from two non-native populations seem capable of maintaining normal health, performance and behavior during immune challenge, a response often referred to as parasite tolerance. Specifically, in Chapter 2, we found that when Floridian house sparrows, established since ~1870, were challenged with synthetic pathogens that mimicked infection with a fungi, an RNA virus or Gram-negative bacteria, only individuals challenged by the synthetic bacteria showed measurable sickness behaviors and secretion of an inflammatory protein. In Chapter 3, we compared parasite tolerance in Kenyan house sparrows (introduced in ~2000) and a native congener, the grey-headed sparrow (P. griseus) to a common intestinal parasite of songbirds. We found that both species were tolerant in that they were able to maintain fat reserves, protein reserves and vertical flight ability during infection. However, house sparrows maintained burdens that were, on average, more than 10x those of grey-headed sparrows. Moreover, when examining nutrient allocation in the two species, house sparrows appeared to assimilate nutrients more efficiently than grey-headed sparrows and did not change how nutrients were allocated among immune and reproductive organs during experimental infection. Grey-headed sparrows, however, did shift nutrient allocation among immune and reproductive organs during experimental infection. Together, the larger nutrient pool and maintenance of nutrient allocation patterns in challenged house sparrows suggests that no physiological trade-offs occurred and that house sparrows experienced a lower cost of parasite exposure. In the fourth Chapter, I explored why house sparrows had such high coccidia burdens in comparison to their congeners. We suspected burden was a function of the frequency of exposure to coccidia. Consequently, we explored heterogeneity in foraging preferences and other behaviors in Floridian house sparrows and their role in coccidia burden. As expected, we found that house sparrows did not avoid contaminated food. In fact, they ate contaminated and uncontaminated foods indiscriminately. What was surprising was a lack of correlation between burden and consumption of contaminated foods and all of the behaviors we monitored (i.e., aggression, activity, feeding rates and defecation frequency). Overall, these data suggest that house sparrows do not benefit from typical parasite-avoidance behaviors. In sum, this dissertation research implies that house sparrows respond to parasite infection differently than many other known vertebrates, most likely in an effort to maximize efficient use of resources and, in so doing, augment competitive ability and invasion success.

The male house sparrows has two assumed visible sexual traits which are 1) the colouration (or brightness) of the beak and 2) the size of the black badge on the bird’s throat and chest. Earlier research has shown that the testosterone concentration play an important part in determine the beak colour, with a higher testosterone concentration giving the bird a darker beak and as such making the male more attractive to females.     Even though stress has been counted for as a changing factor of phenotypes and behaviour it is not certain how vast effect stress has on different animals. This study is focusing on how and if the individuals fundamental stress level (fundamental corticosterone concentration) is affecting the morphological appearance, in this case the visible sexual traits (beak colour and badge size) and mask (an indicator of age), within the house sparrows in the Lundy Island population. In this study there was no relationship between beak colour and corticosterone concentrations, stating that beak brightness is not determined by fundamental stress. Likewise there was no relationship between the corticosterone concentrations and the size of the badge. Mask measurements in relationship to corticosterone showed no significant effect. These results indicate that there is no relationship between the corticosterone concentration in the blood and the mask size or the beak colour and badge size as visible sexual traits. / Många forskare är ense om att gråsparvshannen använder sig av två synliga karaktärsdrag för att attrahera honor. Den första är mörkhetsgraden på näbben och den andra är storleken på hannens svarta bröstlapp, placerad på hals och bröst. Tidigare forskning har visat att näbbfärgen påverkas kraftigt av hannens testosteron nivå och att en högre testosteron nivå leder till en mörkare näbb, vilket är mer attraktivt för honorna.    Även om stress har visat sig påverka både fenotyp och beteende hos många olika djurgrupper är det fortfarande oklart hur stor effekt stress har på olika djur. Denna studie fokuserar på hur och om den individuella fundamentala stressnivån (den fundamentala kortikosteron nivån) påverkar de synliga attraherande karaktärsdragen (näbbfärg och bröstlappsstorlek) hos gråsparvshannarna. I denna rapport analyseras även hannarnas masker, vilka fungerar som åldersindikatorer, i relation till de individuella kortikosteron koncentrationerna. Inget samband kunde hittas mellan näbbfärg och kortikosteron nivå hos de analyserade individerna. Likaså kunde inget samband hittas mellan kortikosteron nivån och storleken på hannens bröstlapp. Inte heller maskstorleken visade samband med kortokosteron nivån. Resultatet indikerar således att stress inte påverkar hannens sexuellt attraktiva karaktärsdrag eller mask.