Sperm competition affects male behaviour and sperm output in the rainbow darter

Rainbow darters, Etheostoma caeruleum, are promiscuous fish with moderate rates of group spawning (between one and five males may simultaneously mate with one female). In this study, I examined male sperm output and male willingness to spawn under different levels of sperm competition intensity. One male and one female were allowed to spawn in an aquarium where they had visual and olfactory access to one of four treatments: four males, one male, zero males, or one female. Theory predicts that males should reduce sperm output when there are more than the average number of males at a group spawning (four-male treatment) and should increase sperm output when there are fewer than average males at a group spawning (one-male treatment). Mean sperm output did not differ among treatments. However, males released more sperm when spawning in the presence of competing males (four-male and one-male treatments pooled) than when spawning in the absence of competing males (zero-male and one-female treatments pooled). Males were also most likely to forego spawning opportunities when sperm competition intensity was high. Furthermore, male willingness to spawn was size dependent. Large males were more likely to forego spawning opportunities under high sperm competition intensity. Large males may be better off waiting for future spawning opportunities when there is a lower potential for sperm competition intensity.     

The effect of acoustic and visual priming stimuli on the reproductive behaviour of female zebra finches, <Emphasis Type="Italic">Taeniopygia guttata</Emphasis>

We investigated the influences of reproductive priming, using acoustic stimuli alone or a combination of acoustic and visual stimuli on egg-laying in female zebra finches (Taeniopygia guttata). One group of females was exposed during 6 days to both acoustic and visual stimuli from males while another was exposed only to acoustic stimuli; a control group was unable to see or hear males prior to the introduction of unfamiliar males for pairing. We also manipulated the amount of visual stimulation by presenting either: males with normal red bands, males with red bands without ultraviolet reflection or unadorned males. Females exposed to visual stimuli spent more time on perches near males than control females or those only hearing males. However, there were no statistically significant differences in subsequent total eggs produced, or the latency to egg-laying between females exposed to priming males with different visual characteristics; they did not significantly differ from the control females in these parameters either. Females that heard, but did not see, priming stimuli produced more eggs when paired with males than the controls. Thus, acoustic stimuli alone may have promoted reproductive condition while the acoustic and visual stimuli together did not. Our results contradict a previous report, and may reflect components of the experimental design we employed (i.e. by pairing females with unfamiliar males after their initial exposure to priming males, we may have suppressed their ability to advance their reproductive state). Females that only heard priming males may have been more willing to accept pairing males because of the absence of visual identifiers.     

A Test for Male Parental Care in a Fundulid, the Bluefin Killifish, Lucania goodei

Under field conditions, breeding male bluefin killifish, Lucania goodei, have been observed aggressively defending territories from other breeding males, non-breeding females, and minnows (mainly Notropis harperi). We performed an aquarium experiment to test whether male aggression serves to protect newly deposited eggs from predation. We allowed a male and a female to spawn in a yarn mop, removed the female, and exposed the eggs to one of four treatments (spawning male present, two minnows present, spawning mal+two minnows present, no adult fish present). Mops were censused daily for seven days. Egg predation rates were highest in the male+minnows and male only treatments. Egg predation rates in the male+minnows treatment did not differ from the predicted predation rate (sum of male only and minnows only treatments). Hence, there is no evidence for male parental care in L. goodei. In addition, we compared the egg predation rates (filial cannibalism) between males of 3 different color morphs and found no evidence for differential egg cannibalism.     

Chemosensory Recognition of Familiar and Unfamiliar Conspecifics by the Scincid Lizard Eumeces laticeps

The ability of broad-headed skinks (Eumeces laticeps) to distinguish familiar from unfamiliar individuals of the opposite sex and themselves from other individuals of the same sex using only chemical stimuli was examined experimentally. Cloacal chemical stimuli were presented to lizards on moistened cotton swabs and numbers of tongue-flicks performed in 60 s were recorded. Males emitted significantly greater numbers of tongue-flicks in response to chemical cues from unfamiliar females than of female cagemates. Response rates of males housed with females and males housed alone to chemical stimuli from unfamiliar females did not differ. Chemical stimuli from unfamiliar males elicited significantly more tongue flicks from males than their own or deionized water, but their own stimuli elicited no more than the odourless control. Females tongue-flicked significantly more in response to cloacal chemical stimuli from unfamiliar males than from male cagemates. The findings indicate that both sexes of broad-headed skinks can discriminate between chemical stimuli of familiar and unfamiliar individuals of the opposite sex and that males can distinguish their own cloacal chemicals from those of unfamiliar males. The possible functions of these chemosensory capacities, including location of mates by scent-trailing and assessment of the presence of sexual competitors, are discussed in relation to the social behaviour of E. laticeps.     

The influence of mechanical, visual and contact chemical stimulation on the behavioural phase state of solitarious desert locusts (Schistocerca gregaria)

We investigated the influence of mechanical, visual and contact chemical stimulation on behavioural gregarization of fifth-instar solitarious nymphs of the desert locust. The stimuli were applied in two 2x2 factorial experimental designs, the first with contact chemical and mechanical stimuli, and the second with contact chemical and visual stimulation. Stimulus treatments were applied for a 4-5 h period, after which the behavioural phase state of individual locusts was measured using an assay based on multiple logistic regression analysis of behavioural variables. Mechanical stimulation was provided by showering test insects with millet seeds, thereby excluding the possibility of contact chemical self-stimulation by repeated contact with the same objects. Visual stimulation consisted of the sight of crowd-reared locusts, while contact chemical stimulation was a dichloromethane extract of cuticular hydrocarbons from gregarious nymphs applied to the perch of the test insect. Mechanical stimulation was powerfully gregarizing, whether alone or in combination with contact chemical stimuli. Application of cuticular extract to the perch had no measurable effect on behavioural phase state, either alone or when presented with mechanical or visual stimuli. Visual stimulation alone partly gregarized test locusts. These results appear to conflict with other reports of the gregarizing effect of cuticular hydrocarbons and possible reasons for this discrepancy are discussed.     

Differing behavioral and endocrinological effects of two female sex pheromones on male goldfish

Ovulatory female goldfish sequentially release at least two sex pheromones: 17 alpha, 20 beta-dihydroxy-4-pregnen-3-one (17,20 beta P) and a mixture of F prostaglandins (PGFs). This study sought to determine whether these pheromones have different endocrinological and behavioral actions and whether the PGF pheromone, which is released by spawning females, is responsible for increasing the gonadotropin (GtH) and milt (sperm and seminal fluid) levels of spawning males. Grouped and isolated males were exposed to combinations of these pheromones, food odor, and spawning and nonspawning females. 17,20 beta P stimulated GtH increases in both grouped and isolated males but had only minor effects on behavior; because its principal function appears to be physiological it may be considered a "primer" pheromone. In contrast, exposue to the PGFs elicited large increases in sexual behavior but increased GtH only when fish were exposed as groups; this pheromone's principal action appears to be behavioral and it should be considered a "releaser" pheromone. Although males had increased GtH and milt levels after 1 hr of spawning, males allowed to interact with nonspawning females also had elevated GtH; thus, behavioral interactions appear capable of elevating GtH in the absence of either pheromone. The existence of an independent behavioral mechanism which stimulates GtH was supported by the fact that males exposed to 17,20 beta P while spawning had GtH levels much greater than males exposed to only one of these stimuli.     

Tactile stimuli perceived by the antennae cause the isolated females to produce gregarious offspring in the desert locust, Schistocerca gregaria

Maternal determination of progeny body size and coloration in the desert locust, Schistocerca gregaria, depends on the crowding conditions experienced during the short sensitive period that occurs two to six days before the deposition of the egg pod. Solitarious (isolated-reared) females produce relatively small eggs that yield solitarious green hatchlings but, females that are exposed to crowded conditions during the sensitive period, produce larger eggs that yield the dark-colored hatchlings characteristic of gregarious forms. The present study aimed to determine the stimuli influencing the maternal determination of progeny characteristics as well as the site at which such stimuli are perceived. By exposing isolated female adults to various combinations of visual, olfactory and tactile stimuli from a crowd of other adults, we found that no crowding effects could be elicited without tactile stimulation. Coating of various body surfaces with nail polish followed by exposure to crowding stimulation suggested that female adults perceive crowding stimuli with their antennae. This finding was supported by another experiment in which the antennae were either removed or covered with wax before the isolated females were exposed to crowded conditions. Neither serotonin nor an antagonist of its receptor affected the density-dependent maternal determination of progeny characteristics when injected into isolated or crowded female adults.     

The effects of visual social stimulation upon age at first spawning in the mouth-brooding cichlid fish Sarotherodon (Tilapia) mossambicus (Peters)

The effect of visual social stimulation upon age at first spawning of Sarotherodon (Tilapia) mossambicus was studied by rearing newly-released young in one of two conditions: isolated or in visual contact with a conspecific of the same age in an adjacent aquarium. Results indicated that isolation delayed first spawning by about 10 days for isolated females as compared to socially stimulated females. The rate of colour development was the same for all males suggesting that testicular maturation was not greatly affected by visual social stimulation. In addition, growth of social females lagged behind that of isolates. Some mechanisms and biological effects are discussed.     

Variation in female guppy preference for male olfactory and visual traits

Animals often use different sensory systems to assess different sexually selected signals from potential mates. However, the relative importance of different signals on mate choice is not well understood in many animal species. In this study, we examined the relative importance of male olfactory and visual cues on female preference in the guppy Poecilia reticulata. We used digitally modified male images to standardize visual stimuli. We found that, regardless of whether females were presented without male visual stimuli or with identical male visual stimuli, they preferred stimuli with the odor of males to those without. However, when females were allowed to choose between dull male visual stimuli with male odor, and brightly colored male visual stimuli without male odor, there was no clear preference for either. Some females preferred the dull male visual stimuli with male odor, whereas some other females preferred the brightly colored male visual stimuli without male odor. These results indicate that the relative importance of olfactory and visual cues in female mate preference varied between individuals.     

The effect of female presence on spermiation, and of male sexual activity on ‘ready’ sperm in the male guppy

This study examines the effect of female presence on the amount of ‘strippable’ sperm, and the relationship between male sexual activity and the amount of ‘ready’ sperm in the male guppy Poecilia reticulata. The amount of strippable sperm was greater in males paired for one week with females than in isolated males. We separated these ‘paired’ males from females by a clear partition and thus exposed males to visual and possibly olfactory stimuli. In the second experiment, control males spent more time attending females and performed more sexual acts during a 15-min test period than males previously stripped of spermatophores. These results indicate that females play an important role in stimulating sperm availability in males and that the amount of ready sperm influences male sexual behaviour. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.      

Demographic Structure,Sex Ratio and Growth Rates of Southern Bluefin Tuna (Thunnus maccoyii) on the Spawning Ground

The demographics of the southern bluefin tuna (SBT) Thunnus maccoyii spawning stock were examined through a large-scale monitoring program of the Indonesian longline catch on the spawning ground between 1995 and 2012. The size and age structure of the spawning population has undergone significant changes since monitoring began. There has been a reduction in the relative abundance of larger/older SBT in the catch since the early 2000s, and a corresponding decrease in mean length and age, but there was no evidence of a significant truncation of the age distribution. Pulses of young SBT appear in the catches in the early- and mid-2000s and may be the first evidence of increased recruitment into the spawning stock since 1995. Fish in these two recruitment pulses were spawned around 1991 and 1997. Size-related variations in sex ratio were also observed with female bias for fish less than 170 cm FL and male bias for fish greater than 170 cm FL. This trend of increasing proportion of males with size above 170 cm FL is likely to be related to sexual dimorphism in growth rates as male length-at-age is greater than that for females after age 10 years. Mean length-at-age of fish aged 8–10 years was greater for both males and females on the spawning ground than off the spawning ground, suggesting that size may be the dominant factor determining timing of maturation in SBT. In addition to these direct results, the data and samples from this program have been central to the assessment and management of this internationally harvested stock.     

Orientation of male gypsy moths,Lymantria Dispar (L.), to pheromone sources: The role of olfactory and visual cues

The role of olfaction and vision in the close-ranging flying and walking orientation of male gypsy moths, Lymantria dispar(L.), to females was studied in the forest and in the laboratory. In the forest, feral males found an isolated pheromone source as readily as one supplemented with female visual cues; dead, acetonerinsed females deployed without pheromone received virtually no visitations. In flight tunnel choice experiments using cylinders as surrogate trees and pheromone in different spatial configurations, visual attributes of the female did not influence either the males' choice of landing site or the efficiency with which they located the female. Rather, the presence of pheromone on the cylinder was necessary to elicit orientation as well as landing and walking on the cylinder. When a female visual model was placed in various positions around a pheromone source, walking males oriented primarily to the chemical stimulus. There were, however, indications that males would alter their walking paths in response to female visual cues over short distances (<5 cm), but only if they continued to receive pheromone stimulation. When visual and chemical cues were abruptly uncoupled by altering the trajectory of the pheromone plume, most males responded to the loss of the odor cue rather than to visual cues from the female. Temporal pheromone stimulation patterns affected male walking orientation. When stimulated by pheromone, males oriented toward the source; loss of the odor cue prompted an arearestricted local search characterized by primarily vertical and oblique movements with frequent reversals in direction. Presumably these maneuvers enhance the likelihood of recontacting the plume or serendipitously encountering the female. The apparent lack of visual response to the female is discussed in light of morphological and behavioral evidence suggesting that gypsy moths were formerly nocturnal.     

Spawning behavior of Arctic charr (Salvelinus alpinus): Spawning synchrony,vibrational communication,and mate guarding

A mismatch in synchrony between male and female gamete release in external fertilizers can result in reduced or failed fertilization, sperm competition, and reduced paternity. In Arctic charr (Salvelinus alpinus), males can adopt either a guard or sneak tactic resulting in both pre‐ and postcopulatory competition between males with alternative reproduction tactics. Here, spawning behavior of free‐living Arctic charr was video‐recorded, and their reproductive behavior was analyzed. From evaluating 157 spawning events, we observed that females mainly spawned with a guarding male and that the female and the guarding male synchronized timing of gamete release under sperm competition. Although sneakers spawned with higher synchrony than the guarding male in single‐male spawning events, the average sneaker released his milt less synchronized with the female than the guarding male under sperm competition. Approximately 50% of the recorded spawning events occurred under sperm competition, where each event included an average of 2.7 males. Additionally, sneakers were more exposed to sperm competition than guarding males. An influx of males, in close proximity to the female, occurred during the behavioral sequences leading up to egg release, but this influx seemed not dependent on egg release, suggesting that something else than gonadal product attracts sneaker males to the spawning female. Just before and during the actual release of gametes, the spawning couple vibrates their bodies in close contact and it seems likely that this vibrational communication between the spawning couple, which results in a larger amplitude sound wave than seen under regular courting, reveals time of gamete release to sneaker males. Thus, vibrational communication may enable synchrony between the guarding male and the female, and this might be traded against the cost of higher detectability from surrounding sneaker males, eavesdropping in close proximity.     

Spawning behavior of the tiger grouper (<Emphasis Type="Italic">Mycteroperca tigris</Emphasis>) in a Caribbean atoll

Many grouper (Epinephelidae) species aggregate to spawn at specific times of year, at consistent locations, and at specific times of day and phases of the moon. The tiger grouper (Mycteroperca tigris) is widely distributed in the Caribbean Sea and aggregates to spawn just after the full moon. In January and February 2003–2005, we conducted visual surveys of a tiger grouper spawning aggregation at Glover’s Reef, Belize. The primary objectives of this study were to describe grouper spawning activities with respect to the timing of the lunar cycle, identify and describe male and female spawning behaviors, and estimate the number of grouper spawning events each day. The peak number of both male and female tiger groupers counted each year occurred from 6 to 10 d after the full moon. The peak count of males was 1.6–2.2 times greater than the peak count of females. Six categories of male–male and six categories of male–female interactions were identified. All male tiger groupers displayed an ability to rapidly change color; this was often triggered by a close encounter with other male or female tiger groupers. The daily spawning activity was remarkably predictable. The first spawning occurred on average 8.1 min before sunset, and the last occurred 5.1 min after sunset. On average, less than half of the females at the spawning site spawned each day, but some females spawned more than once in a given day. Females appeared to choose their mates.     

Male spawning success and female choice in the mottled triplefin,Forsterygion varium (Pisces: Tripterygiidae)

A detailed analysis was made of the variation in spawning success among male Forsterygion (э Tripterygion) varium. The aim was to assess whether females were mating selectively and, if so, to examine the basis of that choice. Eggs were laid on small rocks within the males' territories. Females did not distribute eggs randomly among males. Some males guarded as many as 23000 eggs in one breeding season, while others experienced little or no breeding success. Male spawning success was positively correlated with both their size and some characteristics of their territories, namely the amount of spawning substratum and the presence of a large boulder adjacent to the territory. Experimental manipulations indicated that female choice of males was based on these features. Addition of small rocks into the territories of previously unsuccessful males resulted in a significant increase in spawning success. Conversely, spawning success of the most successful males decreased when small rocks were removed from their territories. When successful males were removed, each territory was occupied by small males; however, there was no significant change in the spawning success of these males. This experiment suggested that, although territory quality was important, female mating decisions could also be influenced by male characteristics such as body size.     

Reproductive coordination in the golden hamster: Female influences on the male

Gonadal regression in male golden hamsters was induced by short day length. Exposure to sexually receptive females living under either long- or short-day conditions failed to induce testicular recrudescence among the males with regressed testes. The combination of long day length and exposure to either sexually receptive females or cages soiled by these females significantly enhanced testicular recrudescence in comparison to males exposed only to long day length. These results indicate that photoperiodic and social stimulation can interact to enhance reproductive functioning in the male hamster and that the social stimuli involved may be chemical cues from the female.     

Decapitated females as a tool in the analysis of Drosophila behaviour

Decapitated females provide a method of arranging variable stimulus environments to evaluate components of behaviour involved in sexual and frequency dependent selection. Conspecific matings are bypassed via male preference for normal females per se. Presence of conspecific decapitatated females induces male to increase insemination of alien females. Discrimination mechanisms, including sign stimuli, are the least labile, and excitability is the most labile component of courtship. D. subpalustris males with abnormal stimulation use a qualitatively different courtship element not present in their normal repertoire. An efficiency index (courtship/insemination) shows D. palustris males, with more heterogenous stimulation in their courtship, more effective in overcoming female reluctance. Sexual isolation may differ operationally from sexual selection in the necessity for particular stimuli rather than more stimulation.     

The effects of supplementary olfactory and auditory stimuli on the stimulus value and mating success of the young boar

The aim of this study was to investigate the stimulus value and mating success of young boars in the presence or absence of exogenous boar-originating stimuli. Ten Large White × Landrace boars were exposed to each of the following treatments at 6 – 7 months of age (Period 1) and again at 9 – 10 months of age (Period 2): (1) no added boar stimuli; (2) added auditory stimuli; (3) added olfactory stimuli; (4) added auditory and olfactory stimuli. The efficacy of each treatment was determined by subjecting each boar to 2 × 5-min mating tests during each age-period, and assessing gilt proceptivity and sexual receptivity. Gilts used in these tests had been ovariectomized and were induced into behavioural oestrus using a threshold dose of oestradiol benzoate.The addition of both exogenous boar-originating stimuli (Treatment 4) significantly (P<0.05) increased gilt proceptivity and sexual receptivity in Period 1. This indicates that young post-pubertal boars may be deficient in both the auditory and olfactory stimulation that they provide to the female pig. No significant differences were observed between treatments during Period 2. These results therefore suggest that young boars (6–7 months of age) may have a lower stimulus value than their older counterparts, and that this may adversely affect mating success.     

Scent of a Dragonfly: Sex Recognition in a Polymorphic Coenagrionid

In polymorphic damselflies discrimination of females from males is complex owing to the presence of androchrome and gynochrome females. To date there is no evidence that damselflies use sensory modalities other than vision (and tactile stimuli) in mate searching and sex recognition. The results of the present behavioural and electrophysiological investigations on Ischnura elegans, a polymorphic damselfly, support our hypothesis that chemical cues could be involved in Odonata sex recognition. The bioassays demonstrate that males in laboratory prefer female to male odour, while no significant difference was present in male behavior between stimuli from males and control. The bioassays suggest also some ability of males to distinguish between the two female morphs using chemical stimuli. The ability of male antennae to perceive odours from females has been confirmed by electrophysiological recordings. These findings are important not only to get insight into the chemical ecology of Odonata, and to shed light into the problem of olfaction in Paleoptera, but could be useful to clarify the controversial aspects of the mating behavior of polymorphic coenagrionids. Behavioural studies in the field are necessary to investigate further these aspects.     

Females Mated without Sperm Transfer Maintain High Sexual Receptivity in the Wolf Spider Schizocosa malitiosa

The mating of the Neotropical lycosid Schizocosa malitiosa is long and complex, involving intense genital stimulation and copulatory courtship. This suggests functions other than just insemination. Previous data indicated that mated females of this species are less sexually receptive than virgins. We hypothesise that copulatory characteristics presented by males during prolonged copulations could be responsible for subsequent female sexual reluctance, and may be selected by cryptic female choice. Our objective was to examine the influence of copulatory behaviour on subsequent female sexual receptivity in S. malitiosa, isolating it from the effects of sperm transfer per se. For this purpose, we obtained males without sperm in their copulatory organs (palpal bulbs), and prevented them from charging their palps by sealing their genital pores immediately after their last moult (treated males). Virgin females were separated into three groups: (i) females exposed once to normal males, (ii) females exposed twice to normal males, and (iii) females exposed first to treated and second to normal males. The results showed that, 3 d after their first mating, females first mated with untreated males were frequently refractory to remating, whereas all those first mated with treated males were receptive. Copulations performed by treated males showed some differences from those performed by normal males, but maintained the basic behavioural pattern with abundant sexual stimulation. The presence of sperm fluids in the female receptacles appears to be the most likely factor generating female remating reluctance. Males may manipulate female responses using receptivity inhibiting substances in their sperm, like those described for insects. Females would first ensure sperm supply, becoming more choosy afterwards. All females, whether mated once or twice, generated similar numbers of progeny, indicating no relationship between number of matings and number of spiderlings.