Samuel C. Andrew

Peak shift in honey bee olfactory learning

If animals are trained with two similar stimuli such that one is rewarding (S+) and one punishing (S−), then following training animals show a greatest preference not for the S+, but for a novel stimulus that is slightly more different from the S− than the S+ is. This peak shift phenomenon has been widely reported for vertebrates and has recently been demonstrated for bumblebees and honey bees. To explore the nature of peak shift in invertebrates further, here we examined the properties of peak shift in honey bees trained in a free-flight olfactory learning assay. Hexanal and heptanol were mixed in different ratios to create a continuum of odour stimuli. Bees were trained to artificial flowers such that one odour mixture was rewarded with 2 molar sucrose (S+), and one punished with distasteful quinine (S−). After training, bees were given a non-rewarded preference test with five different mixtures of hexanal and heptanol. Following training bees’ maximal preference was for an odour mixture slightly more distinct from the S− than the trained S+. This effect was not seen if bees were initially trained with two distinct odours, replicating the classic features of peak shift reported for vertebrates. We propose a conceptual model of how peak shift might occur in honey bees. We argue that peak shift does not require any higher level of processing than the known olfactory learning circuitry of the bee brain and suggest that peak shift is a very general feature of discrimination learning.

Inaccuracies in the history of a well-known introduction: a case study of the Australian House Sparrow ( Passer domesticus )

BackgroundModern ecosystems contain many invasive species as a result of the activity of acclimatisation societies that operated in the second half of the nineteenth century, and these species provide good opportunities for studying invasion biology. However, to gain insight into the ecological and genetic mechanisms that determine the rate of colonization and adaptation to new environments, we need a good understanding of the history of the introduced species, and a knowledge of the source population, timing, and number of individuals introduced is particularly important. However, any inaccuracies in the history of an introduction will affect subsequent assumptions and conclusions.MethodsFocusing on a single well-known species, the House Sparrow (Passer domesticus), we have documented the introduction into Australia using primary sources (e.g. acclimatisation records and newspaper articles).ResultsOur revised history differs in a number of significant ways from previous accounts. Our evidence indicates that the House Sparrow was not solely introduced from source populations in England but also from Germany and most strikingly also from India—with the latter birds belonging to a different race. We also clarify the distinction between the number released and the number of founders, due to pre-release captive breeding programs, as well as identifying inaccuracies in a couple of well-cited sources with respect to the range expansion of the introduced populations.ConclusionsOur work suggests that caution is required for those studying introductions using the key sources of historical information and ideally should review original sources of information to verify the accuracy of published accounts.

The genetic structure of the introduced house sparrow populations in Australia and New Zealand is consistent with historical descriptions of multiple introductions to each country

The house sparrow is one of the most widely introduced vertebrate species around the world, making it an important model species for the study of invasion ecology. Population genetic studies of these invasions provide important insights into colonisation processes and adaptive responses occurring during invasion. Here we use microsatellite data to infer the population structure and invasion history of the introduced house sparrow (Passer domesticus) in Australia and New Zealand. Our results identify stronger population structure within Australia in comparison to New Zealand and patterns are consistent with historical records of multiple introduction sites across both countries. Within the five population clusters identified in Australia, we find declines in genetic diversity as we move away from the reported introduction site within each cluster. This pattern is consistent with sequential founder events. Interestingly, an even stronger decline in genetic diversity is seen across Australia as we move away from the Melbourne introduction site; secondary historical reports suggest this site imported a large number of sparrows and was possible the source of a single range expansion across Australia. However, private allele numbers are highest in the north, away from Melbourne, which could be a result of drift increasing the frequency of rare alleles in areas of smaller population size or due to an independent introduction that seeded or augmented the northern population. This study highlights the difficulties of elucidating population dynamics in introduced species with complex introduction histories and suggests that a combination of historical and genetic data can be useful.

Signs of adaptation to trace metal contamination in a common urban bird

Metals and metalloids at elevated concentrations can be toxic to both humans and wildlife. In particular, lead exposure can act as a stressor to wildlife and cause negative effects on fitness. Any ability to adapt to stress caused by the negative effects of trace metal exposure would be beneficial for species living in contaminated environments. However, mechanisms for responding adaptively to metal contamination are not fully understood in free-living organisms. The Australian populations of the house sparrow (Passer domesticus) provides an excellent opportunity to study potential adaptation to environmental lead contamination because they have a commensal relationship with humans and are distributed broadly across Australian settlements including many long-term mining and smelting communities. To examine the potential for an evolutionary response to long-term lead exposure, we collected genomic SNP data using the house sparrow 200 K SNP array, from 11 localities across the Australian distribution including two mining sites (Broken Hill and Mount Isa, which are two genetically independent populations) that have well-established elevated levels of lead contamination as well as trace metals and metalloids. We contrast these known contaminated locations to other lesser-contaminated environments. Using an ecological association genome scan method to identify genomic differentiation associated with estimates of lead contamination we identified 60 outlier loci across three tests. A total of 39 genes were found to be physically linked (within 20 kbps) of all outliers in the house sparrow reference genome. The linked candidate genes included 12 genes relevant to lead exposure, such as two metal transporters that can transport metals including lead and zinc across cell membranes. These candidate genes provide targets for follow up experiments comparing resilience to lead exposure between populations exposed to varied levels of lead contamination.

Clinal variation in avian body size is better explained by summer maximum temperatures during development than by cold winter temperatures

ABSTRACT Across many taxa, clinal variation in body size has been observed to follow Bergmanns rule, which predicts larger body size in colder climates. For more than a century, this pattern has typically been ascribed to selection for large body size in cold winter climates. Here, in spatially distributed observational data from 30 populations of House Sparrow (Passer domesticus) introduced into Australia and New Zealand, we show that this relationship appears to be explained by a negative relationship with high temperatures during the breeding season. Our results suggest that higher temperatures during the breeding season could reduce body size through developmental plasticity, which should be considered in combination with or as an alternative to selection. Our findings would predict that a hotter climate during breeding could drive significant changes in morphology among populations (and potentially within populations as well, if climate varies temporally across a breeding season). This idea, and our support for it, could account for much of the variation in body size that drives the well-observed patterns first described by Bergmann, and that are still largely attributed to selection on adult body size during cold winters. Understanding the mechanisms behind any climate-dependent developmental plasticity could prove useful for understanding how endotherms may be affected by climate change in the future.

Epigenetic and genetic variation among three separate introductions of the house sparrow (Passer domesticus) into Australia

Invasive populations are often associated with low levels of genetic diversity owing to population bottlenecks at the initial stages of invasion. Despite this, the ability of invasive species to adapt rapidly in response to novel environments is well documented. Epigenetic mechanisms have recently been proposed to facilitate the success of invasive species by compensating for reduced levels of genetic variation. Here, we use methylation sensitive-amplification fragment length polymorphism and microsatellite analyses to compare levels of epigenetic and genetic diversity and differentiation across 15 sites in the introduced Australian house sparrow population. We find patterns of epigenetic and genetic differentiation that are consistent with historical descriptions of three distinct, introductions events. However unlike genetic differentiation, epigenetic differentiation was higher among sample sites than among invasion clusters, suggesting that patterns of epigenetic variation are more strongly influenced by local environmental stimuli or sequential founder events than the initial diversity in the introduction population. Interestingly, we fail to detect correlations between pairwise site comparisons of epigenetic and genetic differentiation, suggesting that some of the observed epigenetic variation has arisen independently of genetic variation. We also fail to detect the potentially compensatory relationship between epigenetic and genetic diversity that has been detected in a more recent house sparrow invasion in Africa. We discuss the potential for this relationship to be obscured by recovered genetic diversity in more established populations, and highlight the importance of incorporating introduction history into population-wide epigenetic analyses.

Higher temperatures during development reduce body size in the zebra finch in the laboratory and in the wild

The most commonly documented morphological response across many taxa to climatic variation across their range follows Bergmanns rule, which predicts larger body size in colder climates. In observational data from wild zebra finches breeding across a range of temperatures in the spring and summer, we show that this relationship appears to be driven by the negative effect of high temperatures during development. This idea was then experimentally tested on zebra finches breeding in temperature‐controlled climates in the laboratory. These experiments confirmed that those individualso produced in a hot environment (30 °C) were smaller than those produced in cool conditions (18 °C). Our results suggest a proximate causal link between temperature and body size and suggest that a hotter climate during breeding periods could drive significant changes in morphology within and between populations. This effect could account for much of the variation in body size that drives the well‐observed patterns first described by Bergmann and that is still largely attributed to selection on adult body size during cold winters. The climate‐dependent developmental plasticity that we have demonstrated is an important component in understanding how endotherms may be affected by climate change.

Signatures of genetic adaptation to extremely varied Australian environments in introduced European house sparrows

Due to its history of multiple introductions to novel environments worldwide, the house sparrow has been used as a model species to study local adaption in invasive avian species. New genomic resources such as a custom 200K SNP array and a house sparrow reference genome provide great prospects for studying rapid local adaptation in this invasive species. Here, we analyse high‐density genomewide genetic data collected across an extensive range of temperate, arid and tropical climates, in Australian populations that were introduced from Europe 150 years ago. We used two population differentiation (PD) and two ecological association (EA) methods to identify putative loci subject to selection across these varied climates. A majority of the outlier SNPs were identified through the use of the latent factor mixed models (LFMM) EA method, but the BayeScEnv EA method had the strongest overlap with the outliers from the two PD methods. Out of all the 971 outliers identified across the different methods, 38.3% were physically linked (within 20 kbps) to 575 known protein‐coding regions in the house sparrow reference genome. Interestingly, some outlier genes had been previously identified in genome scan studies of broadly distributed species or had strong links to traits that are expected to be important to local adaptation, for example, heat‐shock proteins, immune response and HOX genes. However, many outliers still have unknown relevance and some outliers can be false positives. Our results identify an opportunity to use the house sparrow model to further study local adaptation in an invasive species.