Why do female migratory birds arrive later than males?

1. In migratory birds males tend to arrive first on breeding grounds, except in sex-role reversed species. The two most common explanations are the rank advantage hypothesis, in which male-male competition for breeding sites drives stronger selection for early arrival in males than females, and the mate opportunity hypothesis, which relies on sexual selection, as early arrival improves prospects of mate acquisition more for males than for females. 2. To date, theoretical work has focused on selection for early arrival within a single sex, usually male. However, if fitness depends on territory quality, selection for early arrival should operate on both sexes. Here we use two independent modelling approaches to explore the evolution of protandry (male-first arrival) and protogyny (female-first arrival) under the rank advantage and mate opportunity hypotheses. 3. The rank advantage hypothesis, when operating alone, fails to produce consistent patterns of protandry, despite our assumption that males must occupy territories before females. This is because an individual of either sex benefits if it out-competes same-sex competitors. Rather than promoting protandry, the rank advantage mechanism can sometimes result in protogyny. Female-female competition is stronger than male-male competition early in the season, if females compete for a resource (territories occupied by males) that is initially less common than the resource of interest to males (unoccupied territories). 4. Our results support the mate opportunity hypothesis as an explanation of why protandry is the norm in migratory systems. Male-biased adult sex ratios and high levels of sperm competition (modelled as extra-pair young: EPY) both produce protandry as a result of sexual selection. Protogyny is only observed in our models with female-biased sex ratios and low EPY production. 5. We also show that the effects of sex ratio biases are much stronger than those of EPY production, explore the evidence for sex ratio biases and extra-pair paternity in migratory species and suggest future research directions.     

Do plants use airborne cues to recognize herbivores on their neighbours?

Plants show defensive responses after exposure to volatiles from neighbouring plants infested by herbivores. When a plant’s neighbours host only species of herbivores that do not feed on the plant itself, the plant can conserve energy by maintaining a low defence level. An intriguing question is whether plants respond differently to volatiles from plants infested by herbivores that pose greater or lesser degrees of danger. We examined the secretion of extrafloral nectar (EFN) in lima bean plants exposed to volatiles from cabbage plants infested by common cutworm, two-spotted spider mites, or diamondback moth larvae. Although the first two herbivore species feed on lima bean plants, diamondback moth larvae do not. As a control, lima bean plants were exposed to volatiles from uninfested cabbage plants. Only when exposed to volatiles from cabbage plants infested by spider mites did lima bean plants significantly increase their EFN secretion compared with the control. Increased EFN secretion can function as an indirect defence by supplying the natural enemies of herbivores with an alternative food source. Of the three herbivore species, spider mites were the most likely to move from cabbage plants to lima bean plants and presumably posed the greatest threat. Although chemical analyses showed differences among treatments in volatiles produced by herbivore-infested cabbage plants, which compounds or blends triggered the increased secretion of EFN by lima bean plants remains unclear. Thus, our results show that plants may tune their defence levels according to herbivore risk level.     

Do female garter snakes evade males to avoid harassment or to enhance mate quality?

Females of many species behave in ways that make it difficult for males to locate, court, and inseminate them. Two hypotheses have been advanced to explain such behavior: either a female thereby minimizes costs of harassment (sexual conflict model) or by playing "hard to get" she discourages inferior suitors (indirect mate choice model). Our studies of garter snakes (Thamnophis sirtalis parietalis) at a communal den in Manitoba support an interpretation of sexual conflict rather than indirect mate choice. Female snakes dispersed rapidly from the den through areas with relatively few males rather than waiting for additional courtship. Many females dispersed without mating. Experimental (pheromonal) manipulation of the intensity of courtship accelerated rates of female dispersal rather than delaying dispersal, as would be predicted if females wait to obtain matings. The behaviors of females escaping from courting groups were maximally effective in losing their suitors regardless of the number of courting males or whether or not the female was capable of mating (recently mated females cannot mate again because of a mating plug). In total, our data are most consistent with the hypothesis that female garter snakes at communal dens evade males to escape harassment rather than to enhance mate quality.     

Do men yawn more than women?

The aim of this study was to test the hypothesis that sex differences in primate yawning are related to size dimorphism in canine teeth. Data were collected on yawning by a primate species (Homo sapiens) in which the two sexes differ only slightly in canine size. Unlike more dimorphic primates, human males and females did not differ in the frequency of yawning, although uncovered yawns were more frequent in men than in women.     

Do terrestrial gastropods use olfactory cues to locate and select food actively?

Having been investigated for over 40 years, some aspects of the biology of terrestrial gastropod’s olfactory system have been challenging and highly contentious, while others still remain unresolved. For example, a number of terrestrial gastropod species can track the odor of food, while others have no strong preferences toward food odor; rather they find it by random encounter. Here, while assessing the most recent findings and comparing them with earlier studies, the aspects of the food selection based on olfactory cues are examined critically to highlight the speculations and controversies that have arisen. We analyzed and compared the potential role of airborne odors in the feeding behavior of several terrestrial gastropod species. The available results indicate that in the foraging of most of the terrestrial gastropod species odor cues contribute substantially to food finding and selection. The results also suggest, however, that what they will actually consume largely depends on where they live and the species of gastropod that they are. Due to the voluminous literature relevant to this object, this review is not intended to be exhaustive. Instead, I selected what I consider to be the most important or critical in studies regarding the role of the olfaction in feeding of terrestrial gastropods.     

Do house mice use UV cues when foraging?

Research on the behavioural ecology of ultraviolet (UV-A, wavelengths of 320–400 nm, hereafter: UV) sensitivity in terrestrial vertebrates has mainly focused on sexual signalling and foraging in birds and reptiles, whereas the fact that some rodents are also sensitive to UV light has been somewhat ignored. Here, we present the results of two behavioural experiments, which tested whether rodents use UV cues in foraging. In the first experiment we asked whether the colour contrast in the UV waveband is used as a foraging cue. House mice were offered UV-reflecting and UV-absorbing artificial food items in two different illuminations where UV light was either present or absent. The food items were offered to two groups of mice, one group on a UV-reflecting and the other on a UV-absorbing background. The second experiment investigated more specifically whether UV cues are especially important in dawn and dusk when short wavelengths are high in the proportion of available light. House mice showed no preference between the food items regardless of illumination or background. Therefore, our results indicate that house mice do not use UV cues in foraging.     

Do bonobos copulate more frequently and promiscuously than chimpanzees?

The copulatory activities of bonobos (Pan paniscus) of Wamba, Zaire, were compared with those of chimpanzees (P. troglodytes schweinfurthii) of Mahale, Tanzania. The copulation rates of adult male bonobos were equal to or lower than those of adult male chimpanzees. The copulation rates of adult female bonobos were approximately equal to those of adult female chimpanzees who were in maximal genital swelling, but it should be much higher than those of the adult female chimpanzees throughout the birth interval. The copulation rates of adolescent male bonobos were lower than those of adolescent male chimpanzees, whereas the copulation rates of adolescent female bonobos were much higher than those of adolescent female chimpanzees. It was suggested that the bonobos of Wamba did not copulate more promiscuously than did the chimpanzees of Mahale. The female bonobos may show “receptivity”, whereas female chimpanzees may show rather “proceptivity”.     

Luring houseflies (Musca domestica) to traps: do cuticular hydrocarbons and visual cues increase catch?

Abstract.  Houseflies ( Musca domestica L.) are a major pest species of livestock units and landfill sites. Insecticide resistance has resulted in an increased emphasis on lure-and-kill control methods, but the success of this approach relies on the effective attraction of houseflies with olfactory or visual stimuli. This study examined the efficacy of olfactory (cuticular hydrocarbons) or visual (colours and groups of flies) attractants in a commercial poultry unit. Despite simulating the cuticular hydrocarbon profiles of male and female houseflies, we found no significant increase in the number of individuals lured to traps and no sex-specific responses were evident. The use of target colours selected to match the three peaks in housefly visual spectral sensitivity yielded no significant increase in the catch rate of traps to which they were applied. This study also demonstrated that male and female flies possess significantly different spectral reflectance (males are brighter at 320–470 nm; females are brighter at 470–670 nm). An experiment incorporating groups of recently killed flies from which cuticular hydrocarbons were either removed by solvent or left intact also failed to show any evidence of olfactory or visual attraction for houseflies of either sex. This study concluded that variations of the most commonly applied methods of luring houseflies to traps in commercial livestock units fail to significantly increase capture rates. These results support commonly observed inconsistencies associated with using olfactory or visual stimuli in lure-and-kill systems, possibly because field conditions lessen the attractant properties observed in laboratory experiments.     

Do more sociable dogs gaze longer to the human face than less sociable ones?

Domestic dogs (Canis familiaris) are especially skillful in communicating with humans, and they rely on special abilities to do that. One of these skills involves gazing at human faces in cases of uncertainty or when seeking for something out of reach. In this study, we evaluated the relationship between dogs' sociability level and the ability to learn to gaze in a situation with food in sight but out of their reach. Thirty-nine adult dogs were tested in two procedures: (1) a sociability test that involved interacting with an unknown person, and (2) a learning task that consisted of training trials in which gazing at the experimenter's face was food reinforced, followed by extinction trials in which gazing was not followed by food. A significant positive correlation was found between the duration of physical contact with the unknown person in the sociability test and gaze duration during extinction. Moreover, high sociability dogs gazed significantly longer at humans during extinction trials. We discuss the possibility that, more sociable animals, such as those who pay more attention to the person in our sociability test, may be more persistent in their communicative attempts because the presence of the human is intrinsically reinforcing to them. Finally, we comment on the importance of these findings for training purposes.     

Is there more to GABA than synaptic inhibition?

In the mature brain, GABA (gamma-aminobutyric acid) functions primarily as an inhibitory neurotransmitter. But it can also act as a trophic factor during nervous system development to influence events such as proliferation, migration, differentiation, synapse maturation and cell death. GABA mediates these processes by the activation of traditional ionotropic and metabotropic receptors, and probably by both synaptic and non-synaptic mechanisms. However, the functional properties of GABA receptor signalling in the immature brain are significantly different from, and in some ways opposite to, those found in the adult brain. The unique features of the early-appearing GABA signalling systems might help to explain how GABA acts as a developmental signal.     

Do cyclic female goats respond to males with an increase in LH secretion during the breeding season?

The male effect is currently only used during seasonal or lactational anoestrus because the response is thought to be blocked in cyclic females by periods of elevated progesterone. In this study, we tested whether cyclic, female goats would respond to male exposure with an increase in pulsatile LH secretion. During May (breeding season; Southern Hemisphere) the cycles of 16 Australian Cashmere goats were synchronised using intravaginal progesterone pessaries. Pessary insertion was staggered to produce groups in their early luteal (EL; n=8) and late luteal phases (LL; n=8). The LL group was retrospectively subdivided into mid-luteal (ML; n=4) and late luteal (LL; n=4) groups due to differences in oestrous cycle length that emerged during the study. Male exposure stimulated an increase in LH pulse frequency in the EL and LL groups (P<0.01) but not in the ML group (P>0.1). This increase was accompanied by an increase in basal and mean concentrations of LH in the LL group (P<0.05) but not in EL (P<0.1) or ML (P>0.1) group. There was no effect of male exposure on LH pulse amplitude (P>0.1). Progesterone concentrations differed among all groups on the day of male exposure (P<0.05) and declined significantly over the 12-h sampling period in the LL group (P<0.05). Prolactin concentrations declined in the EL group but did not change significantly in the ML or LL group. In conclusion, male exposure induced an increase in pulsatile LH in goats in the early and late luteal phases of the oestrous cycle. The high concentrations of progesterone in females in the mid-luteal phase appeared to block the male effect.     

The Calicotyle conundrum: do molecules reveal more than morphology?

Partial large subunit 28S rDNA sequences were obtained for specimens of Calicotyle (Monogenea: Monocotylidae) from eight different host species distributed worldwide to test the validity of some species and to address the question of host-specificity in others. Sequences obtained for Calicotyle specimens identified as C. kroyeri based on morphological methods from the type-host Raja radiata (Rajidae) and an additional host R. clavata, both from the North Sea, were identical. However, `C. kroyeri' from the cloaca of R. naevus from Tunisia, Raja sp. A from Tasmania and R. radula from Tunisia differed from C. kroyeri from R. radiata by five (0.51%), 21 (2.13%) and 39 (3.96%) base pairs, respectively, over 984 sites. Therefore, it is likely that the specimens from Raja sp. A, R. radula and perhaps even from R. naevus are not C. kroyeri. Molecular results determined that the calicotylines from the cloaca of Urolophus cruciatus and U. paucimaculatus (Urolophidae) from southern Tasmania identified previously as C. urolophi are indeed identical. Large subunit 28S rDNA sequences of C. palombi and C. stossichi collected from the cloaca and rectal gland, respectively of Mustelus mustelus (Triakidae) from the coast of Tunisia differ sufficiently for these calicotylines to be considered separate and valid species. Our results indicate that some species of Calicotyle are not strictly host-specific, but that C. kroyeri may not be as widely distributed in rajids as was believed previously. Calicotyle specimens from rajids must be re-examined critically to determine whether there are morphological differences indicative of specific differences that may have been overlooked previously.     

Do scale-free regulatory networks allow more expression than random ones?

In this paper, we compile the network of software packages with regulatory interactions (dependences and conflicts) from Debian GNU/Linux operating system and use it as an analogy for a gene regulatory network. Using a trace-back algorithm we assemble networks from the pool of packages with both scale-free (real data) and exponential (null model) topologies. We record the maximum number of packages that can be functionally installed in the system (i.e., the active network size). We show that scale-free regulatory networks allow a larger active network size than random ones. This result might have implications for the number of expressed genes at steady state. Small genomes with scale-free regulatory topologies could allow much more expression than large genomes with exponential topologies. This may have implications for the dynamics, robustness and evolution of genomes.     

Why do males of the dance flyEmpis borealis refuse to mate? The importance of female age and size

Empis borealisfemales form swarms, and males carrying a nuptial gift come to swarms to mate. Males either mated with one of the females (accepted swarms) or left swarms without mating (refused swarms). Males mated with the younger (low wing-wear) and relatively larger females in accepted swarms. They seemed to be able to judge the relative size of the females but to ignore their absolute size. Visiting males stayed shorter in accepted swarms as female size variation increased. This probably reflects their greater ease in choosing a mate among females of relatively different sizes. Females in accepted swarms tended to be larger and to have less worn wings than females in rejected swarms.