Latitudinal distribution, migration, and testosterone levels in birds

Tropical bird species usually have lower testosterone (T) levels during breeding than temperate species. However, the potential mechanisms behind the positive interspecific correlation between T and latitude remain unexplored. In a comparative study of more than 100 bird species, we examined whether social constraints during male-male competition arising from migration and breeding synchrony are responsible for the latitude effects. Species that breed at higher latitudes are more likely to migrate and experience more intense intrasexual competition upon spring arrival than nonmigrant species from lower latitudes. Additionally, species from higher latitudes cope with shorter breeding seasons and thus with more synchronous breeding, which selects for high T titers via increased male-male conflicts. Accordingly, peak T levels were associated with migration and the duration of the egg laying period that reflects breeding synchrony. Because migration and breeding synchrony were related to latitudinal distribution, they appear to be important components of the latitude effects on T. A multivariate model controlling for covariation of predictor variables revealed that latitude remained the strongest predictor of peak T. Therefore, selection due to migration and breeding synchrony may partially cause the latitude effect, but other geographically varying factors may also play a role in mediating peak T levels at different latitudes.     

Castration does not decrease nonreproductive aggression in yearling male European starlings (Sturnus vulgaris)

In the nonbreeding season, some bird species express high levels of aggression despite basal plasma testosterone (T) concentrations. Consequently, nonreproductive aggression is believed to be independent of plasma T. In the present study, we investigated the effect of castration on nonreproductive aggressive behavior in yearling male European starlings (Sturnus vulgaris). We paired castrated (Cx) with control (C) males in dyadic trials during three test periods (December, January-February, and March-April), and by using an infrared camera, we defined which male was the most aggressive one when both males were competing over access to a nest box to roost in. During each of the three periods, Cx males behaved more aggressively than C males but differences between groups did not reach significance. When analyzing the results of the three periods together, Cx males were found to be significantly more aggressive than C males. Likewise, when considering only the second and third period (when plasma T levels of C males were significantly higher than those of Cx males) the same result was obtained. Furthermore, in the third period, aggression tended to be lower than in the first and second period, although T concentrations of C males were highest in this period. Our data thus clearly show that nonreproductive aggression in yearling male starlings is independent of gonadal sex steroids and suggest it even increases by castration.     

Female presence affects male behavior and testosterone levels in the European starling (Sturnus vulgaris)

In this study, we confronted individually housed male European starlings (Sturnus vulgaris) with a female conspecific for 60 min to study the consequences on behavior and plasma testosterone (T) concentrations. Control males experienced a similar procedure, the only difference being that they were tested in the absence of a female. Female presence significantly affected both behavior and plasma T levels of male starlings. Experimental males spent significantly more time singing in the nest box and flew significantly more into the nest box with green nesting material during female presentations than during control periods. Control males never showed these mate attraction behaviors. In total 5 of the 16 experimental males did not respond behaviorally to the female stimulus bird (NR males). In contrast to T levels of control males, plasma T concentrations of both experimental males that did respond to the female (R males) and of NR males (which only perceived the female stimulus) were positively influenced by female presentation. The time spent singing in the nest box by experimental males (R and NR males combined) during female presence tended to be positively correlated with changes in plasma T levels. Finally, before introduction of a female, plasma T levels of R males were significantly higher than those of NR males indicating that individually housed males respond to the presence of a female conspecific by increasing their mate attraction behaviors only when a threshold plasma T concentration has been reached.     

Heavy metal pollution affects dawn singing behaviour in a small passerine bird

Although several studies have suggested that behavioural measures may be more comprehensive than other biomarkers for indicating an organism’s health or welfare, this has rarely been investigated in free-living terrestrial vertebrates. Here we examine the expression of dawn singing behaviour in a free-living small songbird in relation to environmental pollution. We compared the singing behaviour of male great tits Parus major inhabiting an area extremely polluted with heavy metals with that of males inhabiting areas of low(er) pollution (at 4 and 20 km distance from the pollution source). Males at the most polluted site had a significantly smaller repertoire size than males at the two other sites. They also produced a significantly lower total amount of song during the dawn chorus than the males at a distance of 4 km from the pollution source. Our results, although non-experimental and obtained in field conditions, strongly suggest that heavy metal pollution might affect the expression of singing behaviour. Taking into account that previous studies were not able to detect clear, straightforward differences between the health of great tits at the most polluted site and at 4 km distance from the pollution source, our results suggest that the singing behaviour of great tits may be a useful indicator of environmental stress at the population level.     

Certain aspects of bonobo female sexual repertoire are related to urinary testosterone metabolite levels

We examined the unknown relationship between testosterone and sexual behaviour in female bonobos (Pan paniscus) on a daily and long-term level. In most animal species, sexual behaviours mainly focus on reproduction. Bonobos, however, also use sexual interactions to a large extent to maintain and restore social relationships. They display an elaborate sexual repertoire that is expressed during fertile as well as non-fertile periods in life and exhibit a high degree of female control over sexual interactions. Using urinary testosterone metabolite levels of cycling and non-cycling females, we found no relationship between daily differences in testosterone metabolite concentrations and any of the sexual behaviours. However, long-term differences in the variables partially confirm the hypothesis of Jurke et al. [2001] stating that in bonobos testosterone is primarily related to non-reproductive sexual interactions. Furthermore, remarkably, a negative correlation of testosterone metabolite levels with the frequency of the females' sexual inspections was demonstrated. No correlation was found with the frequency of sexual presentations performed by the females and with the frequency of masturbation. We present a case study on this topic in an immigrating female.     

Effects of testosterone on song, aggression, and nestling feeding behavior in male great tits, Parus major

As outlined in the trade-off hypothesis of testosterone (T) secretion, fluctuations in T during the breeding season might reflect how males allocate their time and energy to competitive behaviors for mates and territories, associated with high T levels, and parental activities, associated with low T levels. In the present study, great tit, Parus major, males were implanted with T-filled or empty silastic capsules at the start of the breeding season and the behavior of these two male categories was compared during the entire breeding season. As a measure of competitive behavior we looked at song behavior and territorial responsiveness to a male decoy, during the three main stages of the breeding period (the egg-laying, incubation, and nestling stages). As a measure of parental care we looked at feeding behavior during the nestling stage. Our results only partly supported the trade-off hypothesis. T implants increased plasma androgen levels and enhanced spontaneous song activity and the production of aggressive vocalizations in response to a decoy. However, our results suggest that the degree of physical aggression might be less than fully coupled with T. First, approach to the decoy was not affected by the treatment. Second, although T levels are known to vary from high during egg laying to low while feeding young, control and T-treated males spent similar amounts of time close to the decoy in the three breeding stages. Our results thus suggest that vocal and physical aggression might be regulated differently in the great tit. Furthermore, in contrast with most other studies on temperate bird species but in agreement with a previous study on the great tit, T treatment did not affect male feeding rates. As the dose of T we used was lower than that typically used in other studies, we cannot at present completely exclude the possibility that the latter result reflects this lower dose of T rather than the species used.     

Sex roles in nest keeping – how information asymmetry contributes to parent‐offspring co‐adaptation

Parental food provisioning and offspring begging influence each other reciprocally. This makes both traits agents and targets of selection, which may ultimately lead to co‐adaptation. The latter may reflect co‐adapted parent and offspring genotypes or could be due to maternal effects. Maternal effects are in turn likely to facilitate in particular mother‐offspring co‐adaptation, further emphasized by the possibility that mothers are sometimes found to be more responsive to offspring need. However, parents may not only differ in their sensitivity, but often play different roles in postnatal care. This potentially impinges on the access to information about offspring need. We here manipulated the information on offspring need as perceived by parents by playing back begging calls at a constant frequency in the nest‐box of blue tits (Cyanistes caeruleus). We measured the parental response in provisioning to our treatment, paying particular attention to sex differences in parental roles and whether such differences alter the perception of the intensity of our manipulation. This enabled us to investigate whether an information asymmetry about offspring need exists between parents and how such an asymmetry relates to co‐adaptation between parental provisioning and offspring begging. Our results show that parents indeed differed in the frequency how often they perceived the playback due to the fact that females spent more time with their offspring in the nest box. Correcting for the effective exposure of an adult to the playback, the parental response in provisioning covaried more strongly (positive) with offspring begging intensity, independent of the parental sex, indicating coadaptation on the phenotypic level. Females were not more sensitive to experimentally increased offspring need than males, but they were exposed to more broadcasted begging calls. Therefore, sex differences in access to information about offspring need, due to different parental roles, have the potential to impinge on family conflicts and their resolution.     

Relationship of Self-Rated Health to Stroke Incidence and Mortality in Older Individuals with and without a History of Stroke: A Longitudinal Study of the MRC Cognitive Function and Ageing (CFAS) Population

Introduction

Poor self-rated health (SRH) has been associated with increased risk of death and poor health outcomes even after adjusting for confounders. However its’ relationship with disease-specific mortality and morbidity has been less studied. SRH may also be particularly predictive of health outcomes in those with pre-existing conditions. We studied whether SRH predicts new stroke in older people who have never had a stroke, or a recurrence in those with a prior history of stroke.

Methods

MRC CFAS I is a multicentre cohort study of a population representative sample of people in their 65th year and older. A comprehensive interview at baseline included questions about presence of stroke, self-rated health and functional disability. Follow-up at 2 years included self-report of stroke and stroke death obtained from death certificates. Multiple logistical regression determined odds of stroke at 2 years adjusting for confounders including disability and health behaviours. Survival analysis was performed until June 2014 with follow-up for up to 13 years.

Results

11,957 participants were included, of whom 11,181 (93.8%) had no history of stroke and 776 (6.2%) one or more previous strokes. Fewer with no history of stroke reported poor SRH than those with stroke (5 versus 21%). In those with no history of stroke, poor self-rated health predicted stroke incidence (OR 1.5 (1.1–1.9)), but not stroke mortality (OR 1.2 (0.8–1.9)) at 2 years nor for up to 13 years (OR 1.2(0.9–1.7)). In those with a history of stroke, self-rated health did not predict stroke incidence (OR 0.9(0.6–1.4)), stroke mortality (OR 1.1(0.5–2.5)), or survival (OR 1.1(0.6–2.1)).

Conclusions

Poor self-rated health predicts risk of stroke at 2 years but not stroke mortality among the older population without a previous history of stroke. SRH may be helpful in predicting who may be at risk of developing a stroke in the near future.     

Vital and dispensable roles of Plasmodium multidrug resistance transporters during blood‐ and mosquito‐stage development

Multidrug resistance (MDR) proteins belong to the B subfamily of the ATP Binding Cassette (ABC) transporters, which export a wide range of compounds including pharmaceuticals. In this study, we used reverse genetics to study the role of all seven Plasmodium MDR proteins during the life cycle of malaria parasites. Four P. berghei genes (encoding MDR1, 4, 6 and 7) were refractory to deletion, indicating a vital role during blood stage multiplication and validating them as potential targets for antimalarial drugs. Mutants lacking expression of MDR2, MDR3 and MDR5 were generated in both P. berghei and P. falciparum, indicating a dispensable role for blood stage development. Whereas P. berghei mutants lacking MDR3 and MDR5 had a reduced blood stage multiplication in vivo, blood stage growth of P. falciparum mutants in vitro was not significantly different. Oocyst maturation and sporozoite formation in Plasmodium mutants lacking MDR2 or MDR5 was reduced. Sporozoites of these P. berghei mutants were capable of infecting mice and life cycle completion, indicating the absence of vital roles during liver stage development. Our results demonstrate vital and dispensable roles of MDR proteins during blood stages and an important function in sporogony for MDR2 and MDR5 in both Plasmodium species.