Evidence for increased olfactory receptor gene repertoire size in two nocturnal bird species with well-developed olfactory ability

<p>Abstract</p> <p>Background</p> <p>In vertebrates, the molecular basis of the sense of smell is encoded by members of a large gene family, namely olfactory receptor (OR) genes. Both the total number of OR genes and the proportion of intact OR genes in a genome may indicate the importance of the sense of smell for an animal. There is behavioral, physiological, and anatomical evidence that some bird species, in particular nocturnal birds, have a well developed sense of smell. Therefore, we hypothesized that nocturnal birds with good olfactory abilities have evolved (i) more OR genes and (ii) more intact OR genes than closely related and presumably less 'olfaction-dependent' day-active avian taxa.</p> <p>Results</p> <p>We used both non-radioactive Southern hybridization and PCR with degenerate primers to investigate whether two nocturnal bird species that are known to rely on olfactory cues, the brown kiwi (<it>Apteryx australis</it>) and the kakapo (<it>Strigops habroptilus</it>), have evolved a larger OR gene repertoire than their day-active, closest living relatives (for kiwi the emu <it>Dromaius novaehollandiae</it>, rhea <it>Rhea americana</it>, and ostrich <it>Struthio camelus </it>and for kakapo the kaka <it>Nestor meridionalis </it>and kea <it>Nestor notabilis</it>). We show that the nocturnal birds did not have a significantly higher proportion of intact OR genes. However, the estimated total number of OR genes was larger in the two nocturnal birds than in their relatives.</p> <p>Conclusion</p> <p>Our results suggest that ecological niche adaptations such as daily activity patterns may have shaped avian OR gene repertoires.</p

Sex, drugs and mating role: testosterone-induced phenotype-switching in Galapagos marine iguanas

Males of many vertebrate species have flexible reproductive phenotypes and must decide before each mating season whether to adopt sneaker, satellite, or territorial mating tactics. How do males gauge their abilities against others in the population? We tested experimentally whether hormone--behavior feedback loops allow Galapagos marine iguana males to activate their three behavioral phenotypes as predicted by the relative plasticity hypothesis. Territorial males defended small mating areas and had significantly higher plasma testosterone (T) levels (75 � 11 ng/ml) than did satellite males that roamed around territories (64 � 8 ng/ml) or sneaker males that behaved like females within territories (43 � 11ng/ml). In territorial males, temporary pharmacological blockade of T slowed head-bob patrolling, decreased territory size threefold, and reduced the number of females on territories 20-fold. This supports previous data that females may gauge male attractiveness by using head-bob patrolling, here shown to be a T-dependent trait. Control-treated neighbors reacted to the weakening of T-blocked males by increasing head-bob rate fivefold and territory size 1.6-fold, and female numbers increased 2.5-fold. Unmanipulated or control-injected males remained unchanged. Behavioral effects were partly reversed after 7 days. T injections induced satellite males to establish temporary territories, even at unconventional locations. Some T-boosted satellite males suffered serious fighting injuries. T-injected sneakers left female clusters and behaved like larger satellite males that roam around territories. Thus, territorial and mating tactics are activated by T, but experimental (de-) activation at the wrong ontogenetic stage is costly: manipulated males switched phenotype but thereby lowered their access to females. We hypothesize that T levels of males that are based on early-season behavioral interactions influence a males' subsequent phenotypic role. Copyright 2005.activation-organization of phenotypes; mating strategies; relative plasticity hypothesis; testosterone

Low Metabolism and Inactive Lifestyle of a Tropical Rain Forest Bird Investigated via Heart‐Rate Telemetry

Birds in the lowland tropical rain forest are expected to have low energy turnover. Here, we used heart rate telemetry to estimate nighttime resting metabolic rate (RMR), daily energy expenditure (DEE), and locomotor activity of a small, long‐lived tropical rain forest understory bird, the spotted antbird (Hylophylax naevioides). Heart rate was linearly related to oxygen consumption in respirometry measurements that encompassed 96% of heart rates measured in wild birds. Heart rates in the wild ranged from 260 beats/min at night to 824 beats/min during the day, with a mean of 492 beats/min. Compared with temperate‐forest birds of similar body mass, wild spotted antbirds had a low DEE, only 51% of the expected value. Such low metabolism was achieved mainly by being locomotively inactive for 35% of the daytime (i.e., 0 hops or flights/min). On average, spotted antbirds exhibited 1.6 hops or short flights/min during the daytime. In addition, they decreased nighttime RMR in the wild (at ambient temperatures below their thermoneutral zone [TNZ]) to levels equivalent to nighttime RMR in the laboratory at temperatures within their TNZ. This suggests that wild birds reduce their body temperature every night. Our data confirm and extend previous studies showing that tropical passerines have low metabolic rates

Data from: When the sun never sets: diverse activity rhythms under continuous daylight in free-living arctic-breeding birds

Circadian clocks are centrally involved in the regulation of daily behavioural and physiological processes. These clocks are synchronized to the 24 h day by external cues (Zeitgeber), the most important of which is the light–dark cycle. In polar environments, however, the strength of the Zeitgeber is greatly reduced around the summer and winter solstices (continuous daylight or continuous darkness). How animals time their behaviour under such conditions has rarely been studied in the wild. Using a radio-telemetry-based system, we investigated daily activity rhythms under continuous daylight in Barrow, Alaska, throughout the breeding season in four bird species that differ in mating system and parental behaviour. We found substantial diversity in daily activity rhythms depending on species, sex and breeding stage. Individuals exhibited either robust, entrained 24 h activity cycles, were continuously active (arrhythmic) or showed ‘free-running’ activity cycles. In semipalmated sandpipers, a shorebird with biparental incubation, we show that the free-running rhythm is synchronized between pair mates. The diversity of diel time-keeping under continuous daylight emphasizes the plasticity of the circadian system, and the importance of the social and life-history context. Our results support the idea that circadian behaviour can be adaptively modified to enable species-specific time-keeping under polar conditions