Circadian rhythms are not involved in the regulation of circannual reproductive cycles in a sub-tropical bird, the spotted munia

Abstract

Circannual rhythms regulate seasonal reproduction in many vertebrates. The present study investigated whether circannual reproductive phenotypes (rhythms in growth of gonads and molt) were generated independently of the circadian clocks in the subtropical non-photoperiodic spotted munia (Lonchura punctulata). Birds were subjected to light:dark (LD) cycles with identical light but varying dark hours, such that the period of LD cycle (T) equaled 16 h (T16; 12 h L:4 h D), 21 h (T21; 12 h L:9 h D), 24 h (T24; 12 h L:12 h D) and 27 h (T27; 12 h L:15 h D), or to continuous light (LL, 24 h L:0 h D) at ~18°C. During the~21 month exposure, munia underwent at least two cycles of gonadal development and molt; changes in body mass were not rhythmic. This was similar to the occurrence of annual cycles in reproduction and molt observed in wild birds. A greater asynchrony between circannual cycles of gonad development and molt indicated their independent regulation. Females showed reproductive rhythms with similar circannual periods, whilst in males, circannual periods measured between peak gonadal size were longer in T21 and T24 than in T16 or T27. This suggested a sex-dependent timing of annual reproduction in the spotted munia. Also, food availability periods may not influence the circannual timing of reproduction, as shown by the results on the rhythm in gonadal growth and regression in munia under T-photocycles and LL that provided differential light (feeding) hours. Further, a short-term experiment revealed that activity-rest patterns in munia were synchronized with T-photocycles, but were arrhythmic under LL. We conclude that circadian rhythms are not involved in the timing of the annual reproductive cycle in the spotted munia.

Genetic and phenotypic responses to genomic selection for timing of breeding in a wild songbird

“…The role of tau in circannual rhythms (such as seasonal timing) is, however, unclear. Although some studies did not find a link between circadian and circannual rhythms (Agarwal, Mishra, Komal, Rani, & Kumar, ; Budki, Malik, Rani, & Kumar, ), others have found evidence that they are linked (Gwinner, ; Myung et al, ). Therefore, we chose to investigate a possible response in tau in our breeding time selection lines.…”

Scotostimulation of reproductive neural pathways and gonadal maturation are not correlated with hypothalamic expression of deiodinases in subtropical spotted munia

“…Accordingly, we carried out the present study using subtropical spotted munia ( Lonchura punctulata ), which is an estrildid seasonal breeder with a reproductive season extending from July to October . In captivity, circannual cycles of gonadal maturation‐regression and moult have been shown to persist, regardless of the duration of the light or dark period, or the absence of light or darkness altogether: constant darkness (DD) or light (LL) . However, an interaction of the circannual rhythm with the photoperiodic cycle is necessary to synchronise breeding to the calendar year in the wild .…”

“…In captivity, circannual cycles of gonadal maturation‐regression and moult have been shown to persist, regardless of the duration of the light or dark period, or the absence of light or darkness altogether: constant darkness (DD) or light (LL) . However, an interaction of the circannual rhythm with the photoperiodic cycle is necessary to synchronise breeding to the calendar year in the wild . Spotted munia appear to use small increments of 1.5‐2 minutes of daily photoperiod changes around the vernal equinox to synchronise their reproductive cycle to the calendar year .…”

“…When exposed to constant photoperiods (eg 12:12 hour light/dark cycle [12L:12D] or 24:24 hour light/dark cycle [24L:24D]) or to constant light (LL) for about 2 years, circannual testicular and ovarian cycles persisted with a period of 11 months and 10‐13 months, respectively . Similarly, postnuptial moult was found more dispersed in females than in males under these light conditions …”

“…Therefore, we expected (i) a correlation of OPN5 expression with the length of the light period, namely low and high OPN5 mRNA and protein levels under long night (eg, 3L:21D) and long day (eg, 21L:3D), respectively; (ii) high GnRH‐I/NPY and low GnIH/VIP mRNA and protein levels under 3L:21D, and vice versa under 21L:3D; and (iii) high DIO2/ low DIO3 mRNA levels under 3L:21D, and vice versa under 21L:3D. We also expected a sex‐difference in expression patterns, in view of reported differences in the circannual gonadal and moult cycles between male and female spotted munias …”