Birds from deserts generally have lower total evaporative water loss (TEWL), the sum of cutaneous (CWL) and respiratory water loss (RWL), than species from mesic areas. We investigated the role of CWL and RWL as a function of air temperature (T(a)) in hoopoe larks (Alaemon alaudipes) and Dunn's larks (Eremalauda dunni) from the Arabian Desert and skylarks (Alauda arvensis) and woodlarks (Lullula arborea) from temperate mesic grasslands. The proportional contribution of CWL to TEWL in all larks at moderate T(a) ranged from 50% to 70%. At high T(a) (40 degrees -45 degrees C), larks enhanced CWL by only 45%-78% and relied on an increase in RWL by 676%-2,733% for evaporative cooling. Surface-specific CWL at 25 degrees C was 29% lower in the arid-zone species than in the mesic larks. When acclimated to constant T(a), 15 degrees C-acclimated hoopoe larks increased CWL by 22% compared with 35 degrees C-acclimated birds, but the other species did not change CWL. This study is consistent with the hypothesis that larks from deserts have a reduced CWL at moderate and low T(a) but provided no support for the hypothesis that at high T(a) larks from arid regions rely more on CWL than larks from mesic environments. Interspecific differences in CWL cannot be attributed to acclimation to environmental temperature and are possibly the result of genetic differences due to natural selection or of phenotypically plastic responses to divergent environments during ontogeny.

Dietary restriction (DR) and reduced reproduction each extend life span in many species. Females undergoing DR typically experience a reduction in their fecundity, which raises the question of whether the two treatments are actually extending life span in overlapping ways. Life span in lubber grasshoppers has been shown to be increased by DR, and separately by ovariectomy (OVX). Here, we test the combination of these on life span. If life extension by the two treatments are additive, it would suggest that they likely act through separate pathways. The experimental groups were: fully reproductive and fully fed (ShamFD); ovariectomized and fully fed (OVX FD); fully reproductive and restricted diet (ShamDR); and ovariectomized and restricted diet (OVX DR). The median life spans of these groups were: ShamFD = 245 d, OVX FD = 285 d, ShamDR = 286 d, and OVX DR = 322 d. Feeding rate for the OVX FD group was 64% of ad libitum, not significantly different from the 70% of ad libitum that was used for ShamDR. We also measured hemolymph parameters of physiology in these same individuals. Hemolymph levels of vitellogenin (the egg yolk-precursor protein) were increased 5-fold by OVX, but were not affected by DR. In addition, hemolymph total anti-oxidant activity (per μg protein) was significantly reduced by OVX, but was not affected by DR. We show that OVX and DR produce different physiological responses in grasshoppers, despite life extensions and feeding levels that were not significantly different. These data suggest that OVX and DR might extend life span via distinct pathways.

Summary ― The changes in egg production, in broodiness index and in plasma concentrations of LH, prolactin, cestradiol and progesterone were monitored throughout the first period of laying in turkey hens. The hens were subsequently classified according to their ability to express broodiness (33%) and their laying persistency; 25% were out-of-lay by the end of the experiment. A high percentage (67%) of the hens that went out-of-lay had previously been identified as broody. Altogether, a significant (p < < 0.05) physiological stage effect was found when comparing prolactin, cestradiol and progesterone data obtained from short and long laying persistency hens and this stage effect was also significant for oestradiol and progesterone data obtained from broody and non-broody hens. Otherwise, plasma LH concentrations decreased slightly but significantly throughout the laying year in all hens but no significant differences between physiological states were observed, although the decrease was more pronounced in the hens that went out-of-lay. Plasma progesterone concentrations remained stable throughout in laying hens but decreased significantly in broody and/or out-of-lay hens. Plasma prolactin concentrations were maximal between the 5th and 12th week of egg production and the levels observed in laying hens that did not become broody or had a long laying persistency were twice those measured in broody and/or out-of-lay hens. In the meantime, plasma oestradiol concentrations were lower and stable in laying hens, whereas they were higher during the first half of the productive period in broody and short laying persistency hens. These results suggest that, under our experimental conditions, the hormonal profiles of prolactin and cestradiol for a given hen during the first 10 weeks of the laying cycle may provide predictive information for future changes in its physiological status. The inverse relationship that was observed here between high early plasma concentrations of cestradiol and laying persistency is original. In addition, the relationship between the ability to express broodiness and high and low early plasma concentrations of cestradiol and prolactin, respectively, in hens submitted to preventive broody treatment has not been reported previously. Furthermore

Occupation of desert environments often requires evolutionary specialisations that minimise food and water requirements. One physiological adjustment to living in a hot, dry climate that has been found in several laboratory studies of birds is a reduced basal metabolic rate (BMR), which often translates into a diminished rate of evaporative water loss (EWL). In free-living birds, these physiological traits are thought to result in a lower field metabolic rate and water flux. We studied metabolism and water flux of a number of species of Australian parrots, both in the laboratory and in the field. After combining our laboratory data with values from the literature, we performed allometric analyses to search for evolutionary specialisation in metabolism and water flux in desert-adapted parrots. Our data do not support the idea that parrots living in arid environments have a reduced BMR. Field metabolic rates of parrots from western Australia were indistinguishable from those of other nonpasserine birds. Laboratory EWL was significantly lower for parrots living in desert environments than for those occupying more mesic habitats, and often lower than that expected from body size. Some species of parrots that live in desert regions of Australia have evolved mechanisms that reduce EWL, but this does not involve a reduction in BMR. In the field, parrots living in Western Australia had a lower water influx than predicted for nonpasserines, but this did not approach the value often found in other desert-adapted species. Values for the water economy index (water flux in free-living animals relative to their energy metabolism) were among the lowest that have been reported for desert-adapted birds.

Spinifex pigeons (Geophaps plumifera) are one of the few avian species that have evolved the capacity to reside in the hot and dry regions of central and north-western Australia. Previous investigation has revealed that their basal metabolic rate (BMR) equals only 68% of allometric prediction. In this study, we addressed the hypothesis that these birds have a reduced field metabolic rate (FMR) and water influx as a result of their lowered BMR. We measured the FMR and water flux of free-living spinifex pigeons by means of the doubly labelled water method. Although body mass of free-living male and female pigeons differed significantly, with males weighing on average 90.8 +/- 7.7 g (+/- s.d.) and females 80.2 +/- 5.6 g, FMR was statistically indistinguishable between sexes. For sexes combined, FMR averaged 139.9 mL CO2 h-1, or 73.5 kJ day-1, a value 38.7% of allometric expectation. These data support the hypothesis that spinifex pigeons have a markedly reduced FMR, probably, in part, the result of a depressed BMR compared with other birds of similar size. Our phylogenetic analysis of the BMR of pigeons lacked sufficient data to determine whether a reduced BMR in Australian pigeons was the consequence of ecological adaptation or phylogenetic constraint. Water influx ranged from 2.5 to 39.0 mL day-1 and averaged 18.4 mL day-1. Of the total water intake, 83.5% came from drinking; their food, seeds, supplied about 4%. Maintenance metabolism, energy allocated to basal plus thermoregulatory metabolism, accounted for about 67% of the average FMR, indicating that the activity requires relatively low energy expenditure in these birds.