Photoperiod as a proximate factor in control of seasonality in the subtropical male Tree Sparrow, Passer montanus

Abstract

BackgroundMost species of birds exhibit well-defined seasonality in their various physiological and behavioral functions like reproduction, molt, bill color etc. such that they occur at the most appropriate time of the year. Day length has been shown to be a major source of temporal information regulating seasonal reproduction and associated events in a number of avian species. The present study aims to investigate the role of photoperiod in control of seasonal cycles in the subtropical male tree sparrow (Passer montanus) and to compare its responses at Shillong (Latitude 25°34'N, Longitude 91°53'E) with those exhibited by its conspecifics and related species at other latitudes.ResultsInitial experiment involving study of seasonal cycles revealed that the wild tree sparrows posses definite seasonal cycles of testicular volume, molt and bill color. These cycles were found remarkably linked to annual solar cycle suggesting the possibility of their photoperiodic control. To confirm this possibility in the next experiment, the photosensitive birds were exposed to three different light-dark regimes that were close to what they experience at this latitude: 9L/15D (close to shortest day length), 12L/12D (equinox day length) and 14L/10D (close to longest day length) for 18 months. Tree sparrows showed testicular growth followed by regression and development of photorefractoriness, molting and bill color changes only under long daily photoperiods (12 L and 14 L) but not under short daily photoperiod (9 L). Birds, under stimulatory photoperiods, did not show reinitiation of the above responses after the completion of initiation regression cycle even after their exposure to these photoperiods for 18 months. This precludes the possibility of circannual rhythm generation and suggests the involvement of photoperiodic mechanism in control of their seasonal cycles. Further, replacement of body and primary feathers progressed with gonadal regression only under long days suggesting that the two high energy demanding events of reproduction and molt are phased at two different times in the annual cycle of the bird and are photoperiodically regulated. Results of the final experiment involving exposure of photosensitive birds to a variety of photoperiodic treatments (9L/15D, 10L/14D, 11L/13D, 12L/12D, 14L/10D and 16L/8D) for 30 days suggested that the light falling for 11 h or more is important in inducing testicular growth and function in this species.ConclusionThese results clearly indicate that despite of small photofluctuation, subtropical tree sparrows are capable of fine discrimination of photoperiodic information and use day length as a proximate environmental factor to time their seasonal responses similar to their conspecifics and related species at other latitudes suggesting the conservation of photoperiodic control mechanism in them.

Inter‐ and intraspecific variation in body‐ and genome size in calanoid copepods from temperate and arctic waters

“…Calanoid copepods represent a diverse and abundant group, with many key species in marine ecosystems (Bron et al. 2011). Some species have wide latitudinal distribution, others show sequential replacement of related species along thermal gradients with different degree of overlap (Thibault et al.…”

“…2005; Bron et al. 2011). In general, the genome size appears positively correlated with body size (McLaren et al.…”

Photoperiod and circadian rhythmicity in testicular response of the tree sparrow

“…Since in the tree sparrow photorefractoriness develops only after 60 days of long day photostimulation (Dixit and Singh 2011), its onset is unquestionable in the present study which involves only a maximum period of 60 days during the experiment. Further, the bird showed gonadal regression in SD as well as DD precluding the possibility of the involvement of the internal coincidence model within the reproductive system of birds.…”

“…In birds, the gonadal growth and regression are highly seasonal and relate to environmental factors such as resource availability and length of the photoperiod (Wayne et al 1989;Budki et al 2008). The day length has been well-defined as the regulator of different metabolic and reproductive activities in many avian species (Tewary and Dixit 1983;Kumar 1997;Rani et al 2005;Hahn and MacDougall-Shackleton 2008;Dixit and Singh 2011). The change in photoperiod is entirely predictable at given latitude both within and between years and is used as a reliable cue to time the physiological *Corresponding author.…”

Photo-gonadal response of Indian brahminy myna to resonance cycles in different seasons

“…Annual changes in day length serve as proximate cue in timing the reproductive cycle of many subtropical birds (Pavgi & Chandola 1983;Dixit & Singh 2011).The extent of involvement of day length in regulation of gonadal recrudescence-regression cycle however, varies among species (Dawson et al 2001). This variation is attributed to bird's ability to measure length of day at different stages of breeding.…”