Evolution of sex-biased maternal effects in birds. IV. Intra-ovarian growth dynamics can link sex determination and sex-specific acquisition of resources.

The evolutionary importance of maternal effects is determined by the interplay of maternal adaptations and strategies, offspring susceptibility to these strategies, and the similarity of selection pressures between the two generations. Interaction among these components, especially in species where males and females differ in the costs and requirements of growth, limits inference about the evolution of maternal strategies from their expression in the offspring phenotype alone. As an alternative approach, we examine divergence in the proximate mechanisms underlying maternal effects across three house finch populations with contrasting patterns of sex allocation: an ancestral population that shows no sex-biased ovulation, and two recently established populations at the northern and southern boundaries of the species range that have opposite sequences of ovulation of male and female eggs. For each population, we examined how oocyte acquisition of hormones, carotenoids and vitamins was affected by oocyte growth and overlap with the same and opposite sexes. Our results suggest that sex-specific acquisition of maternal resources and sex determination of oocytes are linked in this system. We report that acquisition of testosterone by oocytes that become males was not related to growth duration, but instead covaried with temporal exposure to steroids and overlap with other male oocytes. In female oocytes, testosterone acquisition increased with the duration of growth and overlap with male oocytes, but decreased with overlap with female oocytes. By contrast, acquisition of carotenoids and vitamins was mostly determined by organism-wide partitioning among oocytes and oocyte-specific patterns of testosterone accumulation, and these effects did not differ between the sexes. These results provide important insights into three unresolved phenomena in the evolution of maternal effects - (i) the evolution of sex-specific maternal allocation in species with simultaneously developing neonates of both sexes; (ii) the link between sex determination and sex-specific acquisition of maternal products; and (iii) the evolution of context-dependent modulation of maternal effects.

Context-dependent sexual advertisement: plasticity in development of sexual ornamentation throughout the lifetime of a passerine bird.

Male investment into sexual ornamentation is a reproductive decision that depends on the context of breeding and life history state. In turn, selection for state- and context-specific expression of sexual ornamentation should favour the evolution of developmental pathways that enable the flexible allocation of resources into sexual ornamentation. We studied lifelong variation in the expression and condition-dependence of a sexual ornament in relation to age and the context of breeding in male house finches (Carpodacus mexicanus)--a species that develops a new sexual ornament once a year after breeding. Throughout males' lifetime, the elaboration of ornamentation and the allocation of resources to the development of sexual ornamentation depended strongly on pairing status in the preceding breeding season--males that were single invested more resources into sexual ornamentation and changed ornamentation more than males that were paired. During the initial (post-juvenile) moult, the expression of ornamentation was closely dependent on individual condition, however the condition-dependence of ornamentation sharply decreased throughout a male's lifetime and in older males expression of sexual ornamentation was largely independent of condition during moult. Selection for early breeding favoured greater ornamentation in males that were single in the preceding seasons and the strength of this selection increased with age. On the contrary, the strength of selection on sexual ornamentation decreased with age in males that were paired in the preceding breeding season. Our results reveal strong context-dependency in investment into sexual ornamentation as well as a high flexibility in the development of sexual ornamentation throughout a male's life.

A condition dependent link between testosterone and disease resistance in the house finch.

Testosterone has recently been proposed as a link between male quality and health and the expression of sexual traits. We investigated the relationship between testosterone and measures of the individual condition and health of males in a natural population of house finches (Carpodacus mexicanus). We also conducted a captive experiment in order to test for the effects of testosterone on resistance to coccidia, which is a common parasite of house finches. Free-living males in better condition had higher testosterone levels and lower corticosterone levels than free-living males in poor condition. In our captive experiment, increased testosterone accelerated the rate of coccidial infection as compared with sham-implanted or gonadectomized males. Although the differences were not significant, free-living males infected with coccidia had lower levels of testosterone and higher levels of corticosterone than males that were not infected. Thus, experimentally elevating testosterone levels in captive males resulted in a higher percentage of infected males, while free-living males with coccidial infection had low testosterone levels. This apparent discrepancy between captive and free-living males in the association of testosterone and disease may be explained by the condition dependence of testosterone. These results suggest that the testosterone-dependent sexual traits reliably indicate male overall condition and health and, thus, females could benefit from assessing potential mates based on these traits.

Maintenance of a captive flock of house finches free of infection by Mycoplasma gallisepticum.

Since the beginning of an epidemic of conjunctivitis in wild house finches caused by Mycoplasma gallisepticum (MG), all captive colonies established by capturing free-ranging house finches from the eastern population have also either been infected at the time of capture or developed infection shortly after capture. In an attempt to avoid this infection in captive flocks being maintained for studies of the finches' behavior and ecology, we compared two different flock management strategies and were able to prevent the development of mycoplasmal conjunctivitis with one of the strategies. Single-sex flocks were built by introducing only seronegative wild-caught birds showing no clinical signs of conjunctivitis and covering their outdoor flight cages with netting to prevent interaction with other wild birds although only the female flocks were initially treated with a 6-wk course of tylosin tartrate (0.3 mg/ml). The female flocks never developed conjunctivitis although the disease did develop in the male flocks. Furthermore, serologic assessments of the healthy flock by serum plate agglutination assays for MG indicated that the females remained free of MG infection in the final 7 wk of the study, during which they were unmedicated. We conclude that any low-level MG infection not diagnosed by the initial test for seroconversion was cleared by the prolonged drug treatment.

A comparison of 25 G and 27 G Whitacre needles for caesarean section.

Spinal needles with a pencil-point tip and those of a finer gauge are known to be associated with a lower incidence of postdural puncture headache. This study set out to determine if fine pencil-point needles were acceptably easy to use in routine clinical practice. Two hundred and twelve women undergoing elective Caesarean section were randomly allocated to receive a subarachnoid block using either a 25 G or 27 G Whitacre needle. Factors determining ease of needle use, adequacy of block, incidence of postdural puncture headache, backache and neurological sequelae were assessed. Successful intrathecal injection was achieved in all patients in the 25 G group. Using the 27 G needle, the anaesthetist failed to reach the subarachnoid space in eight patients of which seven subsequently had a successful intrathecal injection with a larger needle. These failures were attributed to excessive needle flexibility which was the only significant difference in ease of use between the 25 G and 27 G needles. In the 25 G group, there was one severe postdural puncture headache which required an epidural blood patch and three mild headaches which resolved spontaneously. There were no postdural puncture headaches in the 27 G group. We conclude that the final choice of needle is a compromise between the ease of use and lower failure rate of the 25 G needle and the, as yet unproven, possibility of a lower incidence of postdural puncture headache with the 27 G needle.