What comes first, the zebra finch or the egg: temperature-dependent reproductive, physiological and behavioural plasticity in egg-laying zebra finches

Abstract

SUMMARY Avian reproduction is generally timed to synchronize chick-rearing with periods of increased food abundance. Consequently, the energetically demanding period of egg production may coincide with periods of lower food availability,fluctuating temperature and more unstable weather. Little is known about the physiological mechanisms underlying temperature-induced variation in egg production. We therefore examined the influence of low ambient temperature(7°C vs 21°C) on reproductive output (e.g. egg mass, clutch size, laying interval, laying rate), daily food consumption and lipid variables in zebra finches Taeniopygia guttata. When faced with egg production at 7°C, laying zebra finches increased energy intake by 12.67 kJ day–1, and were thus able to maintain body condition (e.g. body mass, fat and muscle score) and circulating triacylglyceride at levels comparable to those at 21°C. However, when producing eggs at 7°C,females took longer to initiate egg laying (6.5 vs 6.1 days at 21°C), and ultimately laid fewer eggs (5.5 vs 6.0 eggs) at a slower rate (0.90 eggs day–1vs 0.95 eggs day–1). These temperature-related declines in reproductive output were accompanied by decreases in modal (from 36.6 at 21°C to 24.3 nm at 7°C) and median very low density lipoprotein (VLDL) particle diameter (from 29.6 to 26.4 nm) and in the proportion of VLDL particles that were capable of passing through the pores in the ovary to access the developing ovarian follicles (i.e. particles with diameters between 25 and 44 nm; from 45.90% to 32.55%). However, variation in reproductive output was not related to any static concentration or structural measure of VLDL. Therefore,other temperature-dependent mechanisms must be involved in the physiological processes that regulate reproductive output of passerine birds at low ambient temperatures.

Is there an energetic-based trade-off between thermoregulation and the acute phase response in zebra finches?

“…However, the food consumption of individuals injected with LPS at 15°C was still significantly greater than individuals at 34°C following LPS injection, with the bulk of this energy presumably allocated toward thermoregulation. Zebra finches apparently maintain a constant body mass in the presence of ad libitum food, irrespective of temperature (Salvante et al, 2007). As such, all individuals had similar energetic reserves to allocate to mounting an immune response.…”

Food restriction negatively affects multiple levels of the reproductive axis in male house finches, Haemorhous mexicanus

“…The amount of furcular fat was visually estimated using a scale of 0-5, with 0 for no fat and 5 for bulging fat (Helms and Drury, 1960). As the pectoral muscles are the largest store of protein in birds, their size was estimated using a scale of 0-3, with 0 for concave pectoral muscles and a prominent keel and 3 for convex pectoral muscles that protrude above the keel (Salvante et al, 2007). At each of these three time points, cloacal protuberance width (±0.1 mm) was also measured using digital calipers.…”

Temperature-induced elevation of basal metabolic rate does not affect testis growth in great tits

“…There are several lines of evidence that bird egg laying dates are partly decided according to past ambient temperatures, including that in great tits (McCleery and Perrins, 1998;Meijer et al, 1999;Nager and van Noordwijk, 1995;O'Connor, 1978;Perrins and McCleery, 1989;Salvante et al, 2007;Visser et al, 2003;Visser et al, 1998). From an ecological point of view, this makes sense as bird fitness is closely related to their ability to match their reproduction with the annual, short period of arthropod abundance, which is highly dependent upon temperature (Visser and Holleman, 2001;Visser et al, 2006).…”

“…On the other hand, there are supplementary cues, such as temperature, which enable fine-tuning of responses to initial predictive cues, and also provide short-term predictive information about the environment (Wingfield and Kenagy, 1991). The effect of temperature on the timing of breeding has been well documented (McCleery and Perrins, 1998;Meijer et al, 1999;Nager and van Noordwijk, 1995;O'Connor, 1978;Perrins and McCleery, 1989;Salvante et al, 2007;van Noordwijk et al, 1995;Visser et al, 2003), but the proximate mechanisms that precede the behavioural response to temperature cues are still poorly understood (Dawson, 2007;Visser et al, 2009). The effect of temperature on gonadal growth is one striking example.…”