ORCID Profile
0000-0002-0232-2543
Current Organisation
University of North Carolina at Chapel Hill
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Publisher: Wiley
Date: 26-04-2005
Publisher: Informa UK Limited
Date: 03-05-2013
Publisher: Wiley
Date: 12-2007
Publisher: Wiley
Date: 08-06-2004
Publisher: Wiley
Date: 08-06-2004
Publisher: The Royal Society
Date: 23-02-2022
Abstract: The insulin and insulin-like signalling (IIS) network plays an important role in mediating several life-history traits, including growth, reproduction and senescence. Although insulin-like growth factors (IGFs) 1 and 2 are both key hormones in the vertebrate IIS network, research on IGF2 in juveniles and adults has been largely neglected because early biomedical research on rodents found negligible IGF2 postnatal expression. Here, we challenge this assumption and ask to what degree IGF2 is expressed during postnatal life across amniotes by quantifying the relative gene expression of IGF1 and IGF2 using publicly available RNAseq data for 82 amniote species and quantitative polymerase chain reaction on liver cDNA at embryonic, juvenile and adult stages for two lizard, bird and mouse species. We found that (i) IGF2 is expressed postnatally across amniote species and life stages—often at a higher relative expression than IGF1 , contradicting rodent models (ii) the lack of rodent postnatal IGF2 expression is due to phylogenetic placement, not inbreeding or artificial selection and (iii) adult IGF2 expression is sex-biased in some species. Our results demonstrate that IGF2 expression is typical for amniotes throughout life, suggesting that a comprehensive understanding of the mechanisms mediating variation in life-history traits will require studies that measure both IGFs.
Publisher: Wiley
Date: 25-10-2011
DOI: 10.1111/J.1095-8649.2011.03105.X
Abstract: The presence and distribution of hybrid in iduals and the existence of a hybrid zone between the catadromous Australian bass Macquaria novemaculeata and estuary perch Macquaria colonorum were investigated throughout the range of both species in Australia. Bayesian analyses and genotypic simulations identified 140 putative hybrids (11·5% of the total s le) with varying levels of introgression. Most hybrids were observed in an area extending from the Snowy River to the Albert River suggesting a hybrid zone in the eastern Bass Strait region. Sixteen hybrids, however, were found outside this zone, possibly reflecting the movement of hybrid offspring between estuaries or their inadvertent release during fish stocking programmes. Biparental backcrossing was found to occur suggesting that hybrids were fertile. These results have implications for the management of the extensive stocking programme in M. novemaculeata and for understanding the potential role of habitat degradation and reduced water flow in facilitating hybridization in species with migratory life histories.
Publisher: The Royal Society
Date: 29-01-2008
Abstract: Many animals upregulate metabolism in response to cold. Uncoupling proteins (UCPs) increase proton conductance across the mitochondrial membrane and can thereby alleviate damage from reactive oxygen species that may form as a result of metabolic upregulation. Our aim in this study was to determine whether reptiles ( Crocodylus porosus ) possess UCP genes. If so, we aimed to place reptilian UCP genes within a phylogenetic context and to determine whether the expression of UCP genes is increased during cold acclimation. We provide the first evidence that UCP2 and UCP3 genes are present in reptiles. Unlike in other vertebrates, UCP2 and UPC3 are expressed in liver and skeletal muscle of the crocodile, and both are upregulated in liver during cold acclimation but not in muscle. We identified two transcripts of UCP3, one of which produces a truncated protein similar to the UCP3S transcript in humans, and the resulting protein lacks the predicted nucleotide-binding regulatory domain. Our molecular phylogeny suggests that uncoupling protein 1 (UCP1) is ancestral and has been lost in archosaurs. In birds, UCP3 may have assumed a similar function as UCP1 in mammals, which has important ramifications for understanding endothermic heat production.
Publisher: Springer Science and Business Media LLC
Date: 05-04-2019
Publisher: Wiley
Date: 03-2023
DOI: 10.1002/ECE3.9934
Abstract: The harmful effects of close inbreeding have been recognized for centuries and, with the rise of Mendelian genetics, was realized to be an effect of homozygosis. This historical background led to great interest in ways to quantify inbreeding, its depression effects on the phenotype and flow‐on effects on mate choice and other aspects of behavioral ecology. The mechanisms and cues used to avoid inbreeding are varied and include major histocompatibility complex (MHC) molecules and the peptides they transport as predictors of the degree of genetic relatedness. Here, we revisit and complement data from a Swedish population of sand lizards ( Lacerta agilis ) showing signs of inbreeding depression to assess the effects of genetic relatedness on pair formation in the wild. Parental pairs were less similar at the MHC than expected under random mating but mated at random with respect to microsatellite relatedness. MHC clustered in groups of RFLP bands but no partner preference was observed with respect to partner MHC cluster genotype. Male MHC band patterns were unrelated to their fertilization success in clutches selected for analysis on the basis of showing mixed paternity. Thus, our data suggest that MHC plays a role in pre‐copulatory, but not post‐copulatory partner association, suggesting that MHC is not the driver of fertilization bias and gamete recognition in sand lizards.
Publisher: Elsevier BV
Date: 02-2009
Publisher: Springer Science and Business Media LLC
Date: 12-03-2008
Publisher: The Royal Society
Date: 24-07-2007
Abstract: Sperm storage is a widespread phenomenon across taxa and mating systems but its consequences for central fitness parameters, such as sex ratios, has rarely been investigated. In Australian painted dragon lizards ( Ctenophorus pictus ), we describe elsewhere that male reproductive success via sperm competition is largely an effect of sperm storage. That is, sperm being stored in the female reproductive tract out-compete more recently inseminated sperm in subsequent ovarian cycles. Here we look at the consequences of such sperm storage for sex allocation in the same species, which has genetic sex determination. We show that stored sperm have a 23% higher probability of producing sons than daughters. Thus, shifts in sex ratio, for ex le over the reproductive season, can partly be explained by different survival of son-producing sperm or some unidentified female mechanism taking effect during prolonged storage.
Publisher: Springer Science and Business Media LLC
Date: 2011
DOI: 10.1186/AR3501
Publisher: Wiley
Date: 13-07-2011
Publisher: Wiley
Date: 12-04-2011
Publisher: Wiley
Date: 11-2008
Publisher: Public Library of Science (PLoS)
Date: 22-04-2011
Publisher: The Royal Society
Date: 07-12-2005
Abstract: The evolution of endothermy is one of the most significant events in vertebrate evolution. Adult mammals and birds are delineated from their early ontogenetic stages, as well as from other vertebrates, by high resting metabolic rates and consequent internal heat production. We used the embryonic development of a bird ( Gallus gallus ) as a model to investigate the metabolic transition between ectothermy and endothermy. Increases in aerobic capacity occur at two functional levels that are regulated independently from each other: (i) upregulation of gene expression and (ii) significant increases in the catalytic activity of the main oxidative control enzymes. Anaerobic capacity, measured as lactate dehydrogenase activity, is extremely high during early development, but diminishes at the same time as aerobic capacity increases. Changes in lactate dehydrogenase activity are independent from its gene expression. The regulatory mechanisms that lead to endothermic metabolic capacity are similar to those of ectotherms in their response to environmental change. We suggest that the phylogenetic occurrence of endothermy is restricted by its limited selective advantages rather than by evolutionary innovation.
Publisher: Wiley
Date: 31-01-2008
Publisher: Oxford University Press (OUP)
Date: 24-05-2019
DOI: 10.1093/ICB/ICZ071
Abstract: It is frequently hypothesized that animals employ a generalized “stress response,” largely mediated by glucocorticoid (GC) hormones, such as corticosterone, to combat challenging environmental conditions. Under this hypothesis, erse stressors are predicted to have concordant effects across biological levels of an organism. We tested the generalized stress response hypothesis in two complementary experiments with juvenile and adult male Eastern fence lizards (Sceloporus undulatus). In both experiments, animals were exposed to erse, ecologically-relevant, acute stressors (high temperature or red imported fire ants, Solenopsis invicta) and we examined their responses at three biological levels: behavioral physiological (endocrine [plasma corticosterone and blood glucose concentrations] and innate immunity [complement and natural antibodies]) and cellular responses (gene expression of a panel of five heat-shock proteins in blood and liver) at 30 or 90 min post stress initiation. In both experiments, we observed large differences in the cellular response to the two stressors, which contrasts the similar behavioral and endocrine responses. In the adult experiment for which we had innate immune data, the stressors affected immune function independently, and they were correlated with CORT in opposing directions. Taken together, these results challenge the concept of a generalized stress response. Rather, the stress response was context specific, especially at the cellular level. Such context-specificity might explain why attempts to link GC hormones with life history and fitness have proved difficult. Our results emphasize the need for indicators at multiple biological levels and whole-organism examinations of stress.
Publisher: The Royal Society
Date: 02-2019
Abstract: Behavioural ecologists often use data on patterns of male–female association to infer reproductive success of free-ranging animals. For ex le, a male seen with several females during the mating season is predicted to father more offspring than a male not seen with any females. We explored the putative correlation between this behaviour and actual paternity (as revealed by microsatellite data) from a long-term study on sand lizards ( Lacerta agilis ), including behavioural observations of 574 adult males and 289 adult females, and paternity assignment of more than 2500 offspring during 1998–2007. The number of males that contributed paternity to a female's clutch was correlated with the number of males seen accompanying her in the field, but not with the number of copulation scars on her body. The number of females that a male accompanied in the field predicted the number of females with whom he fathered offspring, and his annual reproductive success (number of progeny). Although behavioural data explained less than one-third of total variance in reproductive success, our analysis supports the utility of behavioural-ecology studies for predicting paternity in free-ranging reptiles.
Publisher: Wiley
Date: 05-12-2006
Publisher: Springer Science and Business Media LLC
Date: 18-11-2006
Publisher: Wiley
Date: 06-06-2013
DOI: 10.1002/JEZ.1803
Abstract: Female sperm storage can influence male reproductive success and may favour males that produce sperm that remain viable across several ovarian cycles. Here we show that sperm are viable in the female reproductive tract across ovarian cycles in the mallee dragon, Ctenophorus fordi. Based on experimental mating trials, we show that stored sperm were generally less likely to fertilize eggs than recently inseminated sperm. The fertilization success of stored sperm increased with male body size relative to rivals. This may be due to differences in ejaculate volume or sperm number transferred by males of different sizes. However, there was no evidence that copulation time, which is correlated with ejaculate volume, contributed to fertilization success. We suggest that sperm storage across ovarian cycles may be common in small, multi-clutched lizards and that its impact on selection on male phenotypes could contribute to the evolution of lizard mating systems.
Publisher: Wiley
Date: 19-10-2022
DOI: 10.1111/MEC.16723
Abstract: Telomeres are nucleotide‐protein caps, predominantly at the ends of Metazoan linear chromosomes, showing complex dynamics with regard to their lengthening and shortening through life. Their complexity has entertained the idea that net telomere length and attrition could be valuable biomarkers of phenotypic and genetic quality of their bearer. Intuitively, those in iduals could be more heterozygous and, hence, less inbred. However, some inbred taxa have longer, not shorter, telomeres. To understand the role of inbreeding in this complex scenario we need large s les across a range of genotypes with known maternity and paternity in telomere‐screened organisms under natural conditions. We assessed the effects of parental and hatchling inbreeding on telomere length in offspring from sires and dams in a population of sand lizards ( Lacerta agilis ). Maternal and paternal ID and their interactions predict hatchling telomere length at substantial effect sizes ( R 2 .50). Deviation from mean maternal heterozygosity statistically predicts shorter offspring telomeres but this only when sibship is controlled for by paternal ID, and then is still limited ( R 2 = .06). Raw maternal heterozygosity scores, ignoring absolute deviation from the mean, explained 0.07% of the variance in hatchling telomere length. In conclusion, inbreeding is not a driver of telomere dynamics in the sand lizard ( Lacerta agilis ) study system.
Publisher: Wiley
Date: 12-10-2009
DOI: 10.1111/J.1755-0998.2009.02718.X
Abstract: Nine polymorphic microsatellite loci were characterized from an enrichment library of the Australian praying mantid Ciulfina rentzi, a group with a unique reproductive morphology and behaviour. The number of alleles per locus ranged from three to 16 and heterozygosity from 0.24 to 0.94. These markers are the first microsatellites developed for any praying mantid. They will be useful for paternity analysis and for population genetic studies in the Wet Tropics World Heritage Region of Australia.
Publisher: Wiley
Date: 23-08-2011
DOI: 10.1111/J.1420-9101.2011.02368.X
Abstract: Hox genes are recognized for their explanatory power of bilateral development. However, relatively little is known about natural variation in, and the evolutionary dynamics of, Hox genes within wild populations. Utilizing a natural population of sand lizards (Lacerta agilis), we screened HoxA13 for genetic variation and an association with incidence of offspring malformations. We found significant effects of parental genetic similarity and offspring sex, and their interaction, on risk of hatching malformed as an offspring. We also found within population genetic variation in HoxA13, and identified a significant effect of a three-way interaction among Hox genotype, parental genetic similarity, and offspring sex on the risk of hatching malformation. Since malformed offspring in this population do not survive to maturity, this study reveals complex and ongoing selection associated with Hox genes in a wild reptile population. Importantly, this demonstrates the utility of natural populations in unveiling microevolutionary processes shaping variation in highly conserved genes.
Publisher: Wiley
Date: 05-11-2010
DOI: 10.1111/J.1558-5646.2010.01152.X
Abstract: A changing climate is expected to have profound effects on many aspects of ectotherm biology. We report on a decade-long study of free-ranging sand lizards (Lacerta agilis), exposed to an increasing mean mating season temperature and with known operational sex ratios. We assessed year-to-year variation in sexual selection on body size and postcopulatory sperm competition and cryptic female choice. Higher temperature was not linked to strength of sexual selection on body mass, but operational sex ratio (more males) did increase the strength of sexual selection on body size. Elevated temperature increased mating rate and number of sires per clutch with positive effects on offspring fitness. In years when the "quality" of a female's partners was more variable (in standard errors of a male sexual ornament), clutches showed less multiple paternity. This agrees with prior laboratory trials in which females exercised stronger cryptic female choice when male quality varied more. An increased number of sires contributing to within-clutch paternity decreased the risk of having malformed offspring. Ultimately, such variation may contribute to highly dynamic and shifting selection mosaics in the wild, with potential implications for the evolutionary ecology of mating systems and population responses to rapidly changing environmental conditions.
Location: United States of America
No related grants have been discovered for Todd Schwartz.