Temperature modulation of photoperiodically induced LH secretion and its termination in Japanese quail (Coturnix coturnix japonica)

Is microevolution the only emergency exit in a warming world? Temperature influences egg laying but not its underlying mechanisms in great tits

Many bird species have advanced their seasonal timing in response to global warming, but we still know little about the causal effect of temperature. We carried out experiments in climate-controlled aviaries to investigate how temperature affects luteinizing hormone, prolactin, gonadal development, timing of egg laying and onset of moult in male and female great tits. We used both natural and artificial temperature patterns to identify the temperature characteristics that matter for birds. Our results show that temperature has a direct, causal effect on onset of egg-laying, and in particular, that it is the pattern of increase rather than the absolute temperature that birds use. Surprisingly, the pre-breeding increases in plasma LH, prolactin and in gonadal size are not affected by increasing temperature, nor do they correlate with the onset of laying. This suggests that the decision to start breeding and its regulatory mechanisms are fine-tuned by different factors. We also found similarities between siblings in the timing of both the onset of reproduction and associated changes in plasma LH, prolactin and gonadal development. In conclusion, while temperature affects the timing of egg laying, the neuroendocrine system does not seem to be regulated by moderate temperature changes. This lack of responsiveness may restrain the advance in the timing of breeding in response to climate change. But as there is heritable genetic variation on which natural selection can act, microevolution can take place, and may represent the only way to adapt to a warming world.

Neuroendocrine regulation of gonadotropin secretion in seasonally breeding birds

Seasonally breeding birds detect environmental signals, such as light, temperature, food availability, and presence of mates to time reproduction. Hypothalamic neurons integrate external and internal signals, and regulate reproduction by releasing neurohormones to the pituitary gland. The pituitary gland synthesizes and releases gonadotropins which in turn act on the gonads to stimulate gametogenesis and sex steroid secretion. Accordingly, how gonadotropin secretion is controlled by the hypothalamus is key to our understanding of the mechanisms of seasonal reproduction. A hypothalamic neuropeptide, gonadotropin-releasing hormone (GnRH), activates reproduction by stimulating gonadotropin synthesis and release. Another hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH), inhibits gonadotropin synthesis and release directly by acting on the pituitary gland or indirectly by decreasing the activity of GnRH neurons. Therefore, the next step to understand seasonal reproduction is to investigate how the activities of GnRH and GnIH neurons in the hypothalamus and their receptors in the pituitary gland are regulated by external and internal signals. It is possible that locally-produced triiodothyronine resulting from the action of type 2 iodothyronine deiodinase on thyroxine stimulates the release of gonadotropins, perhaps by action on GnRH neurons. The function of GnRH neurons is also regulated by transcription of the GnRH gene. Melatonin, a nocturnal hormone, stimulates the synthesis and release of GnIH and GnIH may therefore regulate a daily rhythm of gonadotropin secretion. GnIH may also temporally suppress gonadotropin secretion when environmental conditions are unfavorable. Environmental and social milieus fluctuate seasonally in the wild. Accordingly, complex interactions of various neuronal and hormonal systems need to be considered if we are to understand the mechanisms underlying seasonal reproduction.

Phenology, seasonal timing and circannual rhythms: towards a unified framework

Phenology refers to the periodic appearance of life-cycle events and currently receives abundant attention as the effects of global change on phenology are so apparent. Phenology as a discipline observes these events and relates their annual variation to variation in climate. But phenology is also studied in other disciplines, each with their own perspective. Evolutionary ecologists study variation in seasonal timing and its fitness consequences, whereas chronobiologists emphasize the periodic nature of life-cycle stages and their underlying timing programmes (e.g. circannual rhythms). The (neuro-) endocrine processes underlying these life-cycle events are studied by physiologists and need to be linked to genes that are explored by molecular geneticists. In order to fully understand variation in phenology, we need to integrate these different perspectives, in particular by combining evolutionary and mechanistic approaches. We use avian research to characterize different perspectives and to highlight integration that has already been achieved. Building on this work, we outline a route towards uniting the different disciplines in a single framework, which may be used to better understand and, more importantly, to forecast climate change impacts on phenology.

Evolution of environmental cue response mechanisms: adaptive variation in photorefractoriness

Appropriate timing of transitions between annual cycle stages (reproduction, plumage molt, migration) is critical to fitness for birds living in temporally varying environments. Environmental cue response systems permit birds to orchestrate these transitions. This paper focuses on how photorefractoriness and one neuroendocrine correlate of it (GnRH system plasticity) have evolved to permit appropriate timing of the transition from breeding to plumage molt. Photorefractoriness is defined by two criteria. Criterion 1: photoinduced gonadal regression occurs without any decline in photoperiod. Criterion 2: photoinduced gonadal regression cannot be reversed by increased photoperiod, even continuous light. Through a comparative approach we show that: (1) Loss of Refractoriness Criterion 1 and of GnRH system down-regulation appear to represent adaptive specializations favoring highly temporally flexible or continuous breeding, (2) Refractoriness Criteria 1 and 2 are not always concordant, and Criterion 2 in particular is not well-correlated with degree of temporal reproductive flexibility, (3) occurrence of some cue response traits are better-explained by phylogenetic relationships among taxa than by current reproductive schedules (seasonal, flexible, opportunistic), (4) substantial temporal flexibility can be achieved in a variety of ways besides adaptive modifications of refractoriness, such as relaxation of long-day requirements for reproductive development, and enhancement of non-photic cue responsiveness. These comparisons also highlight fundamental similarities between some of the most opportunistic species and seasonal breeders, such as an autumn reproductive hiatus during molt. Even in the face of substantial environmental unpredictability, selection may often strongly favor regular scheduling of particularly critical life cycle stages such as plumage molt.

Temperature has a causal effect on avian timing of reproduction

Many bird species reproduce earlier in years with high spring temperatures, but little is known about the causal effect of temperature. Temperature may have a direct effect on timing of reproduction but the correlation may also be indirect, for instance via food phenology. As climate change has led to substantial shifts in timing, it is essential to understand this causal relationship to predict future impacts of climate change. We tested the direct effect of temperature on laying dates in great tits (Parus major) using climatized aviaries in a 6-year experiment. We mimicked the temperature patterns from two specific years in which our wild population laid either early ('warm' treatment) or late ('cold' treatment). Laying dates were affected by temperature directly. As the relevant temperature period started three weeks prior to the mean laying date, with a range of just 4 degrees C between the warm and the cold treatments, and as the birds were fed ad libitum, it is likely that temperature acted as a cue rather than lifting an energetic constraint on the onset of egg production. We furthermore show a high correlation between the laying dates of individuals reproducing both in aviaries and in the wild, validating investigations of reproduction of wild birds in captivity. Our results demonstrate that temperature has a direct effect on timing of breeding, an important step towards assessing the implication of climate change on seasonal timing.

Interspecific variation in photo-induced GnRH plasticity among nomadic cardueline finches

Changes in response to photoperiod are of fundamental importance to seasonal cycles in avian reproductive development. In this study we present data on photo-induced changes in gonadotropin-releasing hormone (GnRH) immunoreactivity associated with the development of photorefractoriness in males of 3 closely related species of cardueline finch: common redpoll (Carduelis flammea), pine siskin (C. pinus) and white-winged crossbill (Loxia leucoptera). All are nomadic, mid- to high-latitude breeders with varying levels of reproductive flexibility: redpolls are typically seasonal, pine siskins more flexibly seasonal and white-winged crossbills temporally opportunistic. Males were exposed to either long (20L:4D) or short days (5L:19D), beginning in January, and GnRH was assessed via immunocytochemistry 4.5 months later. Plasma LH, testis size, and molt score were also measured. Significant reductions in the number of irGnRH cells detected, cross-sectional cell area and optical density of these cells occurred in both redpolls and siskins on long, as compared with short, days. These decreases in irGnRH, coupled with spontaneous testicular regression and onset of molt were consistent with the development of absolute photorefractoriness on constant long days. In contrast, the tendency for numbers of GnRH immunopositive cells and mean measures of GnRH immunoreactivity (cell area, optical density and axonal fiber density) to decrease were much more moderate in white-winged crossbills held on long versus short days. Although none of the four measures of GnRH immunoreactivity differed significantly between treatments in crossbills, significant shifts in the frequency distribution of irGnRH neurons to include greater numbers of less immunoreactive cells suggested that antigenic GnRH content was reduced in many cells. These photo-induced shifts in optical densities of GnRH cells in long-day, as compared with short-day crossbills followed, to a lesser extent, the pattern in pine siskins and common redpolls. For all three species, patterns of decrease in GnRH immunoreactivity, gonadal regression and molt suggest that some form of refractoriness to photostimulation develops on constant long days. However, more moderate tendencies for GnRH immunoreactivity to decrease in white-winged crossbills, coupled with limited gonadal regression and molt on long days suggest that absolute photorefractoriness might develop more slowly in this taxon than in others, or alternatively, a condition arises that is more similar to relative photorefractoriness. These data indicate that relatively small differences in the response of the neuroendocrine system to stimulatory cues such as day length may lead to remarkably different capabilities for reproductive flexibility even within a closely related family of birds.

Seasonal change in luteinizing hormone subunit mRNA in Japanese quail and effects of short daylength and low temperature

Changes in pituitary mRNA levels of LHbeta-subunit (LHbeta) and glycoprotein hormone alpha-subunit (common alpha) were investigated in male Japanese quail under natural and laboratory conditions to clarify the mechanisms of seasonal regulation of luteinizing hormone (LH) secretion. In Experiment 1, birds were kept in outdoor cages under natural conditions from August for 12 months. Both LHbeta and common alpha mRNA levels decreased rapidly from August to September, and after a period of low levels from October through January, they began to increase in February and continued to increase until July. There were more pronounced seasonal changes in testicular weight and cloacal protrusion width with large decreases from August to September and increases from March to May. In Experiment 2, birds were kept on laboratory conditions and transferred from long to short daylengths at 20 or 9 degrees C and held for 14 days. Although common alpha mRNA levels, plasma LH concentrations, testicular weight, and cloacal protrusion area decreased on short days without low temperatures, levels of LHbeta mRNA did not change. Short daylengths combined with low temperatures induced testicular regression and caused decrease in all the parameters measured. Low temperatures under long days did not induce any change in the parameters significantly. These results suggest that (1) synthesis as well as secretion of LH is regulated seasonally, (2) short daylength does not suppress LH synthesis completely unless combined with low ambient temperature, and (3) the effect of photoperiod on the endocrine system regulating LH secretion is predominant over the effect of ambient temperature but ambient temperature acts as an environmental cue to terminate reproductive activities at late summer to early autumn in Japanese quail.

Photorefractoriness in turkey breeder hens is affected by age and season

Experiments were conducted to determine if the incidence or temporal characteristics of photorefractoriness (PR) in turkey hens were influenced by age or season. Age effects on PR were determined by comparing characteristics of PR in the same hens through two consecutive lay periods. Seasonal influences on PR were evaluated by comparing characteristics of PR in hens photostimulated into lay at different seasons of the year. The onset of PR was evaluated by the spontaneous cessation of lay. Data were collected from daily egg production records for time to onset of PR, time to spontaneous termination of PR, and time required for the transition from photosensitive to the PR state. Percentage incidence, repeatability between consecutive cycles, and persistence (duration) of PR were calculated. Age did not influence the mean time to onset of PR following photostimulation but did affect percentage incidence. All second-year hens (recycled) expressed PR, whereas 89% of the first-year hens did so. Time to onset of PR was not correlated between first- and second-year (recycled) hens. Most, but not all, first-year (84.4%) and recycled (92%) hens were transiently PR and spontaneously terminated PR after 20 to 21 wk of unchanged photoperiod. Hens photostimulated in the winter (December) had delayed mean time to onset of PR from that observed with hens photostimulated in spring (May) by about 7.7 wk. Percentage incidence of PR and duration of PR were similar in both seasons of the year. It was concluded that age and season could affect PR.

The behavior of the Japanese or domestic quail Coturnix japonica

This paper reviews the literature pertaining to the behavior of the Japanese or domestic quail Coturnix japonica. Details are given of the classification, characteristics, domestication and the economic and research potential of the species. Further sections deal with sensation and perception (including taste and smell, vision and hearing), maintenance behavior (including feeding and drinking, dust bathing and thermoregulation), development and aging (including vocalization, filial imprinting, sexual imprinting, fear and avoidance responses, sexual maturation and aging), adult learning (including habituation, instrumental conditioning, Pavlovian conditioning and observational learning), photoperiodism, reproductive behavior (including courtship and mating, hormonal control and ontogeny of sexual differentiation, and male and female sexual behavior), parental behavior (including nest-site selection and nest building, incubation behavior and its hormonal control, and hen-chick relationships), and aggressive behavior and dominance (including agonistic behavior and the hormonal control of aggressive behavior).

Annual changes in levels of plasma LH and size of cloacal protrusion in Japanese quail (Coturnix coturnix japonica) housed in outdoor cages under natural conditions

Japanese quail of the strain used in our laboratory do not show a complete decrease in levels of circulating luteinizing hormone (LH) concentrations and show no collapse of the testes following their transfer from long to short days under laboratory conditions. Thus, merely manipulating photoperiods in the laboratory does not simulate an annual breeding cycle. To see whether an annual breeding cycle does exist in "our" quail under natural conditions, mature male birds were housed in individual cages and placed on the roof of a building at 35 degrees 45'N, 139 degrees 53'E; day length and ambient temperature were not controlled at all though food and water were continuously supplied. For 16 months blood was collected every week and the area of the cloacal protrusion measured at the time of each blood collection. The results showed that levels of plasma LH and the area of the cloacal protrusion had a clear annual cycle under the natural conditions. To detect more precisely the changes in circulating LH concentrations during spring and autumn, samples were collected every other day. The first significant increase in levels of plasma LH was found when the day length exceeded 12-12.5 hr, though the increase was sporadic and not synchronized among individuals. The results also showed that circulating levels of LH declined significantly in early September starting when the day length was still about 14 hr; this downward trend continued rather steadily to nonbreeding levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Termination of LH secretion in Japanese quail due to high- and low-temperature cycles and short daily photoperiods

Mature male Japanese quail were transferred from 16L:8D (19 degrees) to one of the following combinations of daily light-dark and temperature cycles, 8L:16D (12 hr, 19 degrees:12 hr, 9 degrees), 12L:12D (12 hr, 19 degrees:12 hr, 9 degrees) and 12L:12D (16 hr, 19 degrees:8 hr, 9 degrees). The low temperature is for the middle of the dark period in each treatment. In the control groups, birds were transferred to the same photoperiodic conditions as the experimental groups, but without changes in ambient temperature. Blood samples were collected every other day for 30 days and circulating levels of plasma LH were estimated by radioimmunoassay. Both the change in conditions from 16L:8D to 8L:16D with the temperature lowered for 12 hr and that from 16L:8D to 12L:12D with temperatures lowered in one case for 12 hr and in the other for 8 hr caused a lowering in plasma LH levels in all the birds to reproductively quiescent levels. The cloacal protrusion of all these birds regressed completely. In control groups, however, most if not all the birds remained in active breeding states although the levels of circulating LH decreased to basal breeding levels of 1-2 ng/ml. The results indicated that in addition to a change from long to short days an alternation of high and low temperatures was sufficient supplementary information in causing termination of LH secretion and inducing regression of the gonads and the accessory sex organs in this species.