Patrick A. Thorpe

The antimicrobial properties of chile peppers (Capsicum species) and their uses in Mayan medicine

A survey of the Mayan pharmacopoeia revealed that tissues of Capsicum species (Solanaceae) are included in a number of herbal remedies for a variety of ailments of probable microbial origin. Using a filter disk assay, plain and heated aqueous extracts from fresh Capsicum annuum, Capsicum baccatum, Capsicum chinese, Capsicum frutescens, and Capsicum pubescens varieties were tested for their antimicrobial effects with fifteen bacterial species and one yeast species. Two pungent compounds found in Capsicum species (capsaicin and dihydrocapsaicin) were also tested for their anti-microbial effects. The plain and heated extracts were found to exhibit varying degrees of inhibition against Bacillus cereus, Bacillus subtilis, Clostridium sporogenes, Clostridium tetani, and Streptococcus pyogenes.

MICROBIAL COLONIZATION OF THE CLOACAE OF NESTLING TREE SWALLOWS

Microbes have the potential to be important selective forces in many aspects of avian biology. Microbes can affect fitness as a result of either their pathogenic or beneficial effects on host health. Little is known about the chronology of microbial colonization of nestlings or the effects of microbes on fledgling condition. We set out to (1) characterize the time course of microbial colonization of the cloacae of nestling Tree Swallows (Tachycineta bicolor), (2) examine the relationship between cloacal microbes and fledgling condition, and (3) determine if nest mates had similar assemblages of cloacal microbes. We repeatedly measured nestlings and sampled their cloacal microbes on nestling days 2, 3, 5, 7, 12, 16, and 19. We detected cloacal microbes in nestlings as early as nestling day 2. Colonization of nestlings by microbes began soon after hatching. Nestlings were colonized by more types of microbes and carried heavier loads of most types of microbes as they got older. Cloacal microbes did not affect fledging success. However, plate scores for gram-negative enteric lactose fermentors, which include E. coli, Salmonella spp., and Shigella spp., were positively correlated with a greater degree of wing asymmetry. This relationship suggests that microbes affect fledgling survival because wing asymmetry hinders flying ability, a critical survival skill for these aerial insectivores. Patterns in the assemblages of cloacal microbes within broods suggested host-genetic influences on the colonization of nestlings by microbes, but they also may have reflected the facts that nest mates were fed by the same adults and were raised in the same nests.

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

Data from the North American Breeding Bird Survey (BBS) suggest that populations of aerial insectivorous birds are declining, particularly in northeastern regions of the continent, and particularly since the mid-1980s. Species that use nest boxes, such as Tree Swallows (Tachycineta bicolor), may provide researchers with large data sets that better reveal finer-scale geographical patterns in population trends. We analyzed trends in occupancy rates for ca. 40,000 Tree Swallow nest-box-years from 16 sites across North America. The earliest site has been studied intensively since 1969 and the latest site since 2004. Nest box occupancy rates declined significantly at five of six (83%) sites east of -78° W longitude, whereas occupancy rates increased significantly at four of ten sites (40%) west of -78° W longitude. Decreasing box occupancy trends from the northeast were broadly consistent with aspects of a previous analysis of BBS data for Tree Swallows, but our finding of instances of increases in other parts of the continent are novel. Several questions remain, particularly with respect to causes of these broadscale geographic changes in population densities of Tree Swallows. The broad geographic patterns are consistent with a hypothesis of widespread changes in climate on wintering, migratory, or breeding areas that in turn may differentially affect populations of aerial insects, but other explanations are possible. It is also unclear whether these changes in occupancy rates reflect an increase or decrease in overall populations of Tree Swallows. Regardless, important conservation steps will be to unravel causes of changing populations of aerial insectivores in North America. RESUME. Les donnees provenant du Releve des oiseaux nicheurs (BBS) de l’Amerique du Nord semblent indiquer que les populations d’insectivores aeriens sont en declin, particulierement dans les regions du nord-est du continent et depuis le milieu des annees 1980. Grâce aux especes qui utilisent les nichoirs, comme l’Hirondelle bicolore (Tachycineta bicolor), les chercheurs ont acces a une grande quantite de donnees qui revelent davantage les tendances des populations a l’echelle fine. Nous avons analyse la tendance du taux d’occupation par l’Hirondelle bicolore a partir de 40 000 nichoirs-annees provenant de 16 sites repartis en Amerique du Nord. Le site le plus ancien est suivi intensivement depuis 1969 et le plus recent, depuis 2004. Le taux d’occupation des nichoirs a diminue significativement dans 5 des 6 sites (83 %) situes a l’est du 78° de longitude ouest, tandis qu’il a augmente significativement dans 4 des 10 sites (40 %) a l’ouest du 78° de longitude ouest. La tendance a la baisse de l’occupation observee dans le nord-est concorde dans les grandes lignes avec les resultats d’une analyse anterieure des donnees du BBS pour cette espece, mais les hausses que nous avons observees dans d’autres regions de l’Amerique du Nord s’averent nouvelles. Plusieurs interrogations demeurent, notamment en ce qui a trait aux causes de ces changements dans la densite des populations d’Hirondelles bicolores a grande echelle. Ces vastes tendances geographiques concordent avec l’hypothese de changements climatiques generalises qui toucheraient les aires d’hivernage, de migration ou de nidification, lesquels pourraient affecter differemment les populations d’insectes aeriens, mais d’autres explications sont aussi possibles. En outre, nous ne savons pas si ces changements du taux d’occupation refletent une hausse ou une baisse dans l’ensemble des populations d’Hirondelles bicolores. Neanmoins, pour assurer leur conservation, il sera important d’elucider les causes des changements de populations chez les insectivores aeriens en Amerique du Nord.

MICROBES IN TREE SWALLOW SEMEN

A frequently hypothesized but poorly studied cost of multiple mating in birds is that exposure to pathogenic sexually transmitted microbes (STMs) can lower reproductive success. Conversely, female birds may benefit from high frequencies of copulation and multiple copulation partners if they receive cloacal inoculations of beneficial STMs that can either protect them against future encounters with pathogens and/or serve as therapy against present infection. We examined the semen of 30 male tree swallows (Tachycineta bicolor) in 1998 to determine the presence and prevalence of potential pathogenic and beneficial STMs. Semen was collected directly from males after applying gentle pressure to the cloaca and we used standard microbiological techniques to identify microbes. We found that 19 of 30 samples contained one or more types of microbes. In these 19 positive samples, we isolated both pathogenic and beneficial microbes from 11, only pathogenic microbes from seven, and only beneficial microbes from one. This variation among males suggests that females would benefit from considering a particular males potential as a donor of either pathogenic or beneficial STMs as a criterion for mate choice. There were few significant differences between males with pathogen-infected semen and those without pathogens in their semen in measures of size, morphology, and ectoparasite score and feather damage. Likewise, there were few significant differences between males with beneficial Lactobacilli spp. in their semen and those without Lactobacilli spp. in their semen in measures of size, morphology, and ectoparasite score and feather damage. We were unable to determine if there was a relationship between microbe presence and prevalence on reproductive performance.

Digit Ratios in Green Anolis Lizards (Anolis carolinensis)

The development of tetrapod digits is directed by the Homeobox (Hox) genes. The expression of Hox genes is influenced by exposure to endogenous sex steroids during development so that prenatal exposure to estrogens and androgens positively influences the lengths of digits 2 (2D) and 4 (4D), respectively. Because of this, Manning ( 2002 ) predicted that male tetrapods should have smaller 2D:4D than that of females because males are exposed to higher levels of androgens during development. We measured digits in green anolis lizards (Anolis carolinensis) to (a) test Mannings prediction; (b) compare our results with those of other studies of digit ratios in reptiles and birds to test the phylogenetic constraint hypothesis, which argues that the digit ratios of reptiles and birds should be more similar to each other than either taxa is to mammals because the patterns have been conserved in living diapsids; and (c) compare our results with those of another study of digit ratio in anoles (Chang et al., 2006 ). We did not detect evidence of sexual dimorphism in 2D:4D. Our results did not support either Mannings prediction or the phylogenetic constraint hypothesis. Furthermore, our results did not match those found in Chang et al. ( 2006 ), suggesting that digit ratios in anolis lizards may not be reliable indicators of prenatal exposure to hormones. Anat Rec, 291:433–440, 2008.

Innate Immune Response Development in Nestling Tree Swallows

Abstract We tracked the development of innate immunity in nestling Tree Swallows (Tachycineta bicolor) and compared it to that of adults using blood drawn from nestlings during days 6, 12, and 18 of the ∼20-day nestling period and from adults. Innate immunity was characterized using an in vitro assay of the ability of whole blood to kill Escherichia coli. The ability of whole blood to kill E. coli increased as nestlings matured. Neither this component of innate immunity nor right wing chord length on day18 were as developed as in adults indicating that development of the innate immune system and growth both continued after fledging. Narrow sense heritability analyses suggest that females with strong immune responses produced nestlings with strong immune responses. These data suggest nestling Tree Swallows allocated sufficient energy to support rapid growth to enable fledging by day 18, but that further development of innate immunity occurred post-fledging.

Digit Ratio in Birds

The Homeobox (Hox) genes direct the development of tetrapod digits. The expression of Hox genes may be influenced by endogenous sex steroids during development. Manning (Digit ratio. New Brunswick, NJ: Rutgers University Press, 2002) predicted that the ratio between the lengths of digits 2 (2D) and 4 (4D) should be sexually dimorphic because prenatal exposure to estrogens and androgens positively influence the lengths of 2D and 4D, respectively. We measured digits and other morphological traits of birds from three orders (Passeriformes, house sparrow, Passer domesticus; tree swallow, Tachycineta bicolor; Pscittaciformes, budgerigar, Melopsittacus undulates; Galliformes, chicken, Gallus domesticus) to test this prediction. None were sexually dimorphic for 2D:4D and there were no associations between 2D:4D and other sexually dimorphic traits. When we pooled data from all four species after we averaged right and left side digits from each individual and z‐transformed the resulting digit ratios, we found that males had significantly larger 2D:4D than did females. Tetrapods appear to be sexually dimorphic for 2D:4D with 2D:4D larger in males as in some birds and reptiles and 2D:4D smaller in males as in some mammals. The differences between the reptile and mammal lineages in the directionality of 2D:4D may be related to the differences between them in chromosomal sex determination. We suggest that (a) natural selection for a perching foot in the first birds may have overridden the effects of hormones on the development of digit ratio in this group of vertebrates and (b) caution be used in making inferences about prenatal exposure to hormones and digit ratio in birds. Anat Rec, 2008.

Left-sided Directional Bias of Cloacal Contacts During House Sparrow Copulations

Abstract Most female birds have only a left ovary and associated oviduct. The entry to the oviduct is on the left side of the urodeum of the cloaca. This arrangement may favor males that mount females from the left during copulation if it results in sperm being placed closer to the opening of the oviduct. Therefore, we predicted a left-sided directional bias of cloacal contacts during House Sparrow (Passer domesticus) copulations. Cloacal contacts from the left outnumbered those from the right 74 to 25 (3:1) during 25 bouts of copulation at 11 House Sparrow nests. While this pattern suggests that a left-sided bias in mounting by males during copulation may be related to the asymmetry of the female reproductive tract, it also might be related to brain lateralization.

Repeated sampling affects Tree Swallow semen characteristics

Abstract Male Tree Swallows (Tachycineta bicolor) face intense sperm competition because mated pairs copulate frequently, extra-pair copulations are common, and females store sperm. We examined the effects of repeated sampling on the characteristics of Tree Swallow semen by manually expressing semen from 15 males immediately after capture (T0) and then hourly for 4 h (T1–T4). The semen characteristics of individual males varied in response to repeated sampling. The total number of sperm cells we obtained from each male over the 4-h sampling period varied from 104–107. Semen samples lacking sperm increased from 6.7% of T0 samples to 26.7– 33.3% of subsequent samples. Forty percent of males provided at least one semen sample that lacked sperm. There were no significant differences among hourly samples in semen volume, sperm concentration, or in the total number of sperm cells obtained from each male. However, there were significant differences among males in each of these variables. Semen volumes represented small proportions of cloacal protuberance volumes. We did not detect significant correlations between total semen volumes or total number of sperm cells obtained from males from T0–T4 and cloacal protuberance volumes. Total semen volume and number of sperm cells obtained from T0–T4 significantly increased with date. However, sperm concentration was not significantly correlated with date. We did not detect significant correlations between semen characteristics and male morphology. Individual variation in responses to repeated sampling has implications for the copulatory strategies of male and female Tree Swallows.

INDIVIDUAL, TEMPORAL, AND SEASONAL VARIATION IN SPERM CONCENTRATION IN TREE SWALLOWS

Abstract We determined sperm concentrations in Tree Swallows (Tachycineta bicolor) by manually expressing semen samples from males during prelaying, egg-laying, incubation, and nestling periods. Sperm concentrations varied by orders of magnitude (0–109 sperm mL−1) among males. Sperm concentrations were highest during the incubation period and lowest during the prelaying period. None of the samples collected during the prelaying, egg-laying, and incubation periods were devoid of sperm. In contrast, 45% of samples collected during the nestling period lacked sperm. Sperm concentrations (1) did not vary over the course of the morning during prelaying, egg-laying, and incubation periods but significantly increased during the nestling period; (2) did not vary with the date that samples were collected during prelaying, egg laying, and incubation but significantly decreased with date during the nestling period; and (3) did not vary with the number of fertile females at the study site during any part of the breeding season. We hypothesize that the variations in sperm concentration arose from a combination of factors including intrinsic differences among males, daily patterns of sperm depletion associated with copulation, and an end-of-season decline in sperm production. If males vary in sperm availability then female Tree Swallows may benefit from pursuing extra-pair copulations as fertility insurance. Variación Individual, Temporal y Estacional en la Concentración de Esperma en Tachycineta bicolor Resumen. Determinamos la concentración de esperma en Tachycineta bicolor tomando manualmente muestras de semen de machos durante los periodos de pre-puesta, puesta de huevos, incubación y con pichones. La concentración de esperma varió en órdenes de magnitud (0–109 esperma por mL) entre machos. Las concentraciones de esperma fueron mayores durante el periodo de incubación y menores durante el periodo de pre-puesta. Todas las muestras colectadas durante los periodos de pre-puesta, puesta e incubación contuvieron esperma. En contraste, el 45% de las muestras colectadas durante el período con pichones no contuvieron esperma. Las concentraciones de esperma (1) no variaron durante el curso de la mañana en los periodos de pre-puesta, puesta e incubación, pero aumentaron significativamente durante el periodo con pichones; (2) no variaron con la fecha en la que las muestras fueron colectadas durante los periodos de pre-puesta, puesta e incubación, pero disminuyeron significativamente con la fecha durante el periodo con pichones; y (3) no variaron durante toda la estación reproductiva con el número de hembras fértiles en el sitio de estudio. Hipotetizamos que esta variación en la concentración de esperma se originó de una combinación de factores incluyendo diferencias intrínsecas entre machos, patrones diarios de vaciamiento de esperma asociados con la cópula, y una disminución al final de la estación en la producción de esperma. Si los machos varían en la disponibilidad de esperma, entonces las hembras de T. bicolor se beneficiarían de obtener copulaciones extra-pareja para asegurar la fertilidad.