Coal TitParus ater song repertoires and the Beau Geste hypothesis

At least 44 different song types were recorded in a population of Coal Tits at Klaebu in central Norway. Each male sang up to 14 different types. In testing the Beau Geste hypothesis the following predictions were made: (1) Territorial males tend to change song type when moving from one song post to another. (2) The tendency to change song type when moving from one song post to another increases with the distance between the song posts. (3) Territory holders prefer inconspicuous song posts that reduce the chances of being instantly detected by possible intruders and prospectors. However, none of these predictions were confirmed by the data analyses. The singing behaviour of the Coal Tit does therefore not support the Beau Geste hypothesis.

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Zusammenfassung In einer Population der Tannenmeise bei Klaebu, Mittelnorwegen, wurden mindestens 44 unterschiedliche Gesangstypen registriert. Einzelne Männchen sangen bis zu 14 Typen. Um die Beau-Geste-Hypothese (ein Sänger täuscht durch verschiedenen Gesangstypen die Anwesenheit mehrerer Individuen vor) zu testen, wurden folgende Annahmen geprüft: (1) Territoriale Männchen neigen dazu, ihren Gesangstyp zu ändern, wenn sie die Singwarte wechseln. (2) Die Tendenz, zwischen Gesangstypen zu wechseln, ist bei Männchen am größten, die während einer Gesangsphase mehr als eine Singwarte benutzen. (3) Territoriale Männchen benützen unauffällige Singwarten, um nicht so schnell von möglichen Eindringlingen oder reviersuchenden Artgenossen entdeckt zu werden. Die Analyse der Daten ergab jedoch für keine dieser Annahmen eine Bestätigung. Somit unterstützt das Verhalten singender Tannenmeisen die Hypothese nicht.

     

A test of the good-genes-as-heterozygosity hypothesis using red-winged blackbirds

Brown recently proposed that the "good genes" that females pursuewhen choosing mates may be individual heterozygosity becausemore heterozygous mates sire offspring with higher fitness.Further, because heterozygosity might enhance developmentalstability, males with more heterozygosity are recognized bythe reduced fluctuating asymmetry (FA) of their bilaterallypaired traits. We used a point sample of 67 male red-winged blackbirds(Agelaius phoeniceus) to test two predictions of this hypothesis:(1) males with more heterozygosity have higher fitness, and(2) males with more heterozygosity have lower FA. We identified7 polymorphic loci from an initial screening of 16 enzymes;32 individuals were completely homozygous, and 35 individualswere heterozygous at at least 1 locus. Larger and older malesrealized higher mating success in this population, but neither sizenor age was related to heterozygosity. Heterozygous males werenot in better condition than homozygous males, nor were theyless infected by hematozoa, lice, or mites. Among 1-year oldmales, epaulet length did not differ between homozygotes andheterozygotes, but among older males, heterozygotes did havelonger epaulets. Homozygotes and heterozygotes did not differin their mean FA scores for nine individual characters. Althoughthe two groups of males did differ in composite FA, heterozygousmales were less symmetrical. Interestingly, this differencewas attributable to a single allele at the PGM-3 locus. Combinedwith previous results showing that FA was generally unrelatedto male health, viability, parental care, social dominance,or mating success, the present results indicate that Brown's hypothesisdoes not explain mate choice or male quality in this populationof red-winged blackbirds.     

Song repertoires and seasonal song in the yellowhammer, Emberiza citrinella

Songs were recorded from male yellowhammers, Emberiza citrinella, in England and West Germany. Sonagraphic analysis revealed three major types of song structure in both populations. Most males had a repertoire of two distinct song types, and sharing between individuals was extremely rare. Most song is produced late in the breeding season, and playback experiments confirmed that it is correlated with an increase in territorial aggression at this time. Some speculations are advanced concerning the origins and functions of song repertoires in the yellowhammer.     

Ontogeny of catabolic and morphological properties of skeletal muscle of the red-winged blackbird (Agelaius phoeniceus)

Thermogenic capabilities of red-winged blackbirds improve markedly during their 10-12-day nestling period, especially between day 5 and day 8. The time course of improvements may be determined by the maturation of skeletal muscles involved in shivering thermogenesis, particularly the pectoralis muscles. To test this hypothesis, morphological and biochemical changes in pectoral and leg muscles were measured in young and adult blackbirds. Both muscles grew disproportionately relative to body mass. The pectoralis consisted entirely of fast-twitch fibers, predominantly fast oxidative glycolytic. In contrast, the gastrocnemius muscle consisted of a mixture of slow and fast fibers (predominantly fast glycolytic). Although fiber composition was constant, both cross-sectional area and density of fibers increased with age in both muscles. Catabolic capacities of the pectoralis increased significantly (approximately 7-8-fold) throughout the nestling period, most abruptly after day 3 (citrate synthase, CS) or day 4 (3-hydroxacyl-CoA-dehydrogenase, HOAD). Myofibrillar ATPase activities in the pectoralis were initially low, but increased after day 5. Further increases in CS and myofibrillar ATPase activities occurred in the pectoralis after fledging. CS and HOAD activities in the leg were much lower, but myofibrillar ATPase activities were remarkably similar in the two muscles, differing only in adults. These results are consistent with the hypothesis that the development of endothermy is dependent on the morphological and biochemical maturation of skeletal muscles important in thermogenesis.     

Size-assortative pairing in Gammarus pulex (Crustacea: Amphipoda): a test of the timing hypothesis

We present the first empirical test of the timing hypothesis regarding the generation of size-assortative pairing in amphipods. The timing hypothesis proposes that, since large males are better able to afford the costs of mate guarding than small males, the former can take larger females into precopula earlier in the female moult cycle than is feasible for the latter. This leaves small males to form pairs with smaller females closer to moult, thus generating size assortment. We presented male Gammarus pulex, collected both in precopula and as singletons, with females that were (1) previously guarded and therefore near to copulatory moult and (2) previously unguarded and therefore far from copulatory moult. This comparison tested the prediction of the timing hypothesis, that size assortment should break down when the opportunity for time-based male decisions is removed, but that size assortment should occur where timing is not disrupted. Counter to the hypothesis, we found that size assortment did not break down upon removal of the time factor. Large males tended to initiate mate guarding earlier than small males in both female moult groups. However, only in the previously unguarded group did large males guard for longer than small males. This result suggests that, although size assortment occurred in all groups, the causative mechanisms that generated this pattern may differ between these groups. We therefore consider the possible importance of mechanisms such as aggression, simultaneous manipulation of females and female resistance in producing size assortment where males encounter numerous females that are close to moult. We also observed that prior recent guarding experience by males had no effect on latency to guard or size-assortative pairing. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Plasma LH and androgen levels in the red-winged blackbird (Agelaius phoeniceus) treated with a potent GnRH analogue.

1. Low doses of GnRH-A (0.01-0.10-1.0 micrograms) given during the annual testes growth period did not clearly affect plasma LH and androgen levels 10 min following the injection. 2. The first injection of high doses of GnRH-A (2.0-10.0-20.0 micrograms) markedly increased plasma LH and androgen levels measured 10 min following the injection. The increase in plasma LH level was dose-dependent and the maximal LH level was obtained with 10.0 micrograms of GnRH-A. 3. Impairment of the LH response to GnRH-A was assessed by comparing the first and the fourteenth injection of high doses of GnRH-A. Evidences of pituitary gland desensitization are reported since plasma LH levels were reduced following the fourteenth injection in all groups. 4. Plasma androgen levels following high doses of GnRH-A were not clearly affected in red-winged blackbirds.     

An observational and brood-exchange sudy of paternal provisioning in the red-winged blackbird, Agelaius phoeniceus

Male red-winged blackbirds (Agelaius phoeniceus) provisioned50%(118/235) of available broods over an 8-year period. In mostcases, each male provisioned only the oldest brood on his territory,but in 21 cases, the male fed a younger brood after first feedingan older one. In 10 of these cases the switch to the youngerbrood followed predation of the older brood, but in the remaining11 cases the cause of the switch was unknown. To determine whethermale red-winged blackbirds adjust their provisioning when thedemands of their broods change, we exchanged broods betweenpairs of nests on 10 territories. Before each exchange, eachmale had been feeding nestlings of only one of the two broods.In response to the exchanges, male (and female) red-winged blackbirdsimmediately adjusted their rates of provisioning to the increasedor decreased demands of the broods. In addition, most malesswitched their provisioning within a day after the exchangeso that they fed the same broods as before the exchanges. Ourresults show that male red-winged blackbirds adjust their provisioningwhen the demands of their broods change and suggest that maleshave enough information about other nesting attempts on theirterritories to shift to a more profitable brood when the expectedbenefits of provisioning change. Male red-winged blackbirdsdo not appear to follow an investment strategy based on priorinvestments (i.e., they do not commit the "Concorde fallacy").     

Maternally derived yolk testosterone enhances the development of the hatching muscle in the red-winged blackbird Agelaius phoeniceus

Hatching asynchrony in avian species often leads to the formation of a size hierarchy that places last-hatched nestlings at a significant disadvantage. The hatching muscle (musculus complexus) is responsible for breaking the shell during hatching and for dorsal flexion of the neck during begging. An increase in its strength in last-hatched nestlings could mitigate the effects of hatching asynchrony by reducing the time required for hatching or enhancing the effectiveness of begging for parentally delivered food or both. We have previously found that yolk testosterone concentration increases with laying order in the red-winged blackbird Agelaius phoeniceus. In this study, we investigated the hypothesis that yolk testosterone has anabolic effects on the development of the complexus, thereby influencing competition among asynchronously hatched nestlings. We found that both yolk testosterone concentration and relative complexus mass (complexus mass/nestling body mass) increased with laying order and that these two variables were positively correlated in both newly hatched nestlings and in two-day-old broods. Moreover, direct injections of testosterone into egg yolks resulted in an increase in relative complexus mass, while injections of flutamide, a testosterone antagonist, resulted in a decrease in relative complexus mass. Neither yolk testosterone concentration nor relative complexus mass differed between male and female nestlings.     

The vocal repertoires of the bush dog (Speothos venaticus), crab-eating fox (Cerdocyon thous), and maned wolf (Chrysocyon brachyurus)

The vocalizations of the bush dog (Speothos venaticus), crab-eating fox (Cerdocyon thous), and maned wolf (Chrysocyon brachyurus) were studied in a captive setting. The three species' repertoires were similar and included whines, long-distance calls, and growls. The whines and growls varied in amplitude, duration, and repetition rate; these variations and the frequencies of occurrence probably were influenced by both social organization and habitat characteristics. The bush dog, which lives in family groups and inhabits rain forests, had an elaborate whine-scream continuum that at close distances conveyed a wide range of moods. On the other hand, the maned wolf, which is solitary and frequents open pampas, used amplitude variations of the growl to signal hostile intentions over short, medium, and long distances.The long-distance vocalizations of the three species were the least variable in structure; the bush dog and crab-eating fox used the call to promote contact with separated pairmates or family members. Based on recordings during development, these two calls appeared to arise from the repetitive whine, a variant of the basic whine syllable. The maned wolf also had a contact-promoting howl, apparently an extended whine of high amplitude, but it was rarely recorded during the present study. More prominent was the maned wolf roar-bark, which functioned to space individuals over large distances, and appeared to be a growl of high amplitude.     

Geographical variation in sperm morphology in the red-winged blackbird (<Emphasis Type="Italic">Agelaius phoeniceus</Emphasis>)

Many species differ genetically, physiologically, and morphologically between geographically distinct populations, typically in response to variation in ecological and climatic variables. Little is known, however, about geographical variation in sperm morphology. Sperm morphology is under strong sexual selection, has been shown to evolve rapidly, and often co-varies with other reproductive traits (e.g., testis size or mating system) that differ between populations in some species. The aim of this study was to establish whether sperm morphology varies between populations of the red-winged blackbird (Agelaius phoeniceus), a species with an enormous breeding range and marked inter-population variation in both body size and mating system. We found (1) highly significant variation in sperm morphology among study sites, (2) a gradual increase in sperm length from the southwest to the northeast of the breeding range, and (3) a strong negative association between sperm length and body size. However, the relationship with the mating system remains unclear. Several hypotheses to explain these patterns are proposed.     

Bioluminescence in firefly larvae: A test of the aposematic display hypothesis (Coleoptera: Lampyridae)

We investigated the hypothesis that bioluminescence in firefly larvae (Coleoptera: Lampyridae) functions as an aposematic display. In two experiments, we confirmed the distastefulness of firefly larvae, and tested the hypothesis that a naive, nocturnal predator can learn to use light signals as aposematic cues for avoiding distasteful prey. Larvae were rejected as acceptable prey by 100% of the house mice (Mus musculus) tested. Mice learned to avoid bitter food associated with light cues significantly faster (P=0.003) than mice presented with food lacking light cues. We conclude that luminescent glowing in firefly larvae meets the requirements of an aposematic signal.     

A test of the sympatric host race formation hypothesis in Neodiprion (Hymenoptera: Diprionidae)

Theory suggests that sympatric speciation is possible; however, its prevalence in nature remains unknown. Because Neodiprion sawflies are host specialists and mate on their hosts, sympatric speciation via host shifts may be common in this genus. Here, we test this hypothesis using near-complete taxonomic sampling of a species group, comprehensive geographical and ecological data, and multiple comparative methods. Host-use data suggest that host shifts contributed to the evolution of reproductive isolation in Neodiprion and previous work has shown that gene flow accompanied divergence. However, geographical data provide surprisingly little support for the hypothesis that host shifts occurred in sympatry. While these data do not rule out sympatric host race formation in Neodiprion, they suggest that this speciation mode is uncommon in the genus and possibly in nature.     

A test of crypsis and predator avoidance in the stonefly Paragnetina media (Plecoptera: Perlidae)

Few studies have considered whether cryptic coloration is protective. As a model predator/prey system, the visually foraging fish rainbow trout, Salmo gairdneri, and the stonefly nymph were used to examine cryptic coloration and anti-predator behaviour of prey. In both the laboratory and field, stonefly nymphs selected dark substrates on which they were inconspicuous and therefore less vulnerable to predation by trout. In the laboratory, substrate colour selection by nymphs ceased approximately 2 h after the lights were turned off but resumed within 1 h of lights being turned on. Stoneflies also selected dark patches, rather than light, on the surface of multi-coloured substrate. Colour selection behaviour was not different in the presence versus absence of trout. Stoneflies perceived colour through a combination of visual input from their compound eyes and oceli.     

A test of the reserve meristem hypothesis using Verbascum thapsus (Scrophulariaceae)

The reserve meristem hypothesis predicts that latent meristems may act as a bet-hedging strategy given high-cost, predictable herbivory. Under this hypothesis, damage to a plant should elicit greater branching. This prediction was tested in Verbascum thapsus with three experiments manipulating the intensity and type of damage to reproductive tissue. In the first experiment, seed set was prevented in the treatment group by stigma excision and lanolin application to 80% of the flowers of each plant. In the second experiment, a minimum of two mating pairs of weevils were added to treated plants prior to the onset of flowering. In the third experiment, all fruits were sliced lengthwise twice. All three treatments significantly reduced seed set. In the first two experiments, treated plants significantly increased degree of branching (branch number and total branch length). This supports the reserve meristem hypothesis as an explanation for greater branching in larger plants of V. thapsus. Interestingly, the fruit destruction experiment failed to elicit a branching response, which suggests that the timing of damage is important.