Selection on learning performance results in the correlated evolution of sexual dimorphism in life history

The evolution of learning can be constrained by trade‐offs. As male and female life histories often diverge, the relationship between learning and fitness may differ between the sexes. However, because sexes share much of their genome, intersexual genetic correlations can prevent males and females from reaching their sex‐specific optima resulting in intralocus sexual conflict (IaSC). To investigate if IaSC constraints sex‐specific evolution of learning, we selected Caenorhabditis remanei nematode females for increased or decreased olfactory learning performance and measured learning, life span (in mated and virgin worms), reproduction, and locomotory activity in both sexes. Males from downward‐selected female lines had higher locomotory activity and longer virgin life span but sired fewer progeny than males from upward‐selected female lines. In contrast, we found no effect of selection on female reproduction and downward‐selected females showed higher locomotory activity but lived shorter as virgins than upward‐selected females. Strikingly, selection on learning performance led to the reversal of sexual dimorphism in virgin life span. We thus show sex‐specific trade‐offs between learning, reproduction, and life span. Our results support the hypothesis that selection on learning performance can shape the evolution of sexually dimorphic life histories via sex‐specific genetic correlations.     

Ovicidal activity of noviflumuron when fed to adult German cockroaches (Dictyoptera: Blattellidae)

Ovicidal activity of the benzoylphenylurea noviflumuron was evaluated in the laboratory on three adult groups (virgin females, virgin males, and fertilized, nongravid females) of the German cockroach, Blattella germanica (L.), through ingestion of treated bait. Novifumuron caused significant ovicidal effects at concentrations ranging from 10 to 5000 ppm after 5-d feeding exposure to virgin and fertilized females. Untreated females produced little or no viable oothecae when mated with virgin males that had previously ingested bait (5-d exposure) with 1000 ppm or 5000 ppm noviflumuron. The highest tested concentration of noviflumuron (5000 ppm) caused 100% ovicidal activity through two ovarian cycles for all three adult groups. Noviflumuron seems to have broader ovicidal activity against B. germanica than reported for other benzoylphenylurea insecticides and can potentially impact cockroach populations through a combination of nymphal mortality and ovicidal activity.     

Relation between circulating sex steroid concentrations and sexual behaviour during pregnancy and post partum in the domestic rabbit

Sexual behaviour of 16 female and 12 male rabbits was studied during pregnancy and early post partum. The main behavioural events of the male (nuzzling and mounting) did not differ in the presence of receptive or non-receptive females. When introduced into the cage of the male, receptive and non-receptive females flattened to the floor or circled around. Sexual receptivity to males decreased in early pregnancy and increased to a maximum a few days around parturition; on Days 1 and 6 post partum, all experimental rabbits submitted to mating. Two groups of females were distinguished: one group submitting to mating whatever the stage of pregnancy, the second being receptive only during the few days before parturition or post partum. During pregnancy and early post partum there was no relation between the colour of the vulva and the female sexual behaviour. Does remained sexually receptive even when progesterone concentrations were high. Nevertheless, the number of receptive females was higher when progesterone concentrations decreased around parturition and the mean daily progesterone values were consistently higher in non-receptive than in receptive females. Oestrogen concentrations during pregnancy were very low and were not related to receptive behaviour.     

Disinhibition of oocyte growth in adult,virgin Periplaneta americana by corpus allatum denervation: Age dependency and relatedness to mating

Unilateral section of the nervi corporis allati I (NCA-1) of isolated, starved, adult, virgin Periplaneta americana disinhibited oocyte growth during a specific period following their adult emergence. The effect required that the corpus allatum (CA) be free of NCA-1 innervation for 4 days beyond the time the females were 7–8 days old. The onset of this sensitive period corresponds to when most isolated, starved virgins become sexually receptive. The results suggest that NCA-1 inhibition of CA activity, initiated about 7 days, is relieved by mating. When done on sexually receptive, starved virgins, unilateral NCA-1 section was as effective as insemination for stimulating growth and chorionation of the first generation of oocytes. Neural inhibition of juvenile hormone (JH) secretion by the CA may also explain diminished production of oocytes by isolated, fed virgins, for during 30 days following unilateral NCA-1 section they produced 2.6 to 5 times more oothecae than did controls with a single CA removed or after the sham operation. The number of oothecae deposited by fed virgins was similarly increased after bilateral NCA-1 section, but to a lesser extent than when the operation was done on fed, inseminated females of the same age. Specificity of the response of the CA to denervation was substantiated by experiments in which the CA were extirpated and reimplanted, by topically applying C₁₆JH, and by experiments in which the nervus corporis cardiaci 1 and 2 on the right or left side were severed.     

Sex ratio and female sexual status of the coconut pest, Oryctes monoceros (Coleoptera: Dynastidae), differ in feeding galleries and pheromone-baited traps

Oryctes monoceros is a serious coconut pest, causing up to 40% damage in tropical Africa. Synthetic aggregation pheromone, ethyl 4-methyloctanoate, has been used to lure adults to traps. Traps with pheromone plus decaying palm material captured a high proportion of males. This raises the question whether individuals, which damage palms are receptive to the pheromone. We studied the sex ratio of the insects feeding on coconuts and those attracted to pheromone traps. Sixty two percent of adults from feeding galleries on living coconut palms were females. Pheromone with rotting palm material lured 43% females. To investigate the reasons for this difference, we compared the reproductive system of females lured to the odour traps or feeding in coconut galleries, or present in old rotting stems. Ninety six percent of the females trapped by pheromone had mated, and were sexually mature. In the galleries on living palms, 46% of females were immature, and 24% had not mated. In old rotting stems where eggs are laid and larvae develop, a mixture of 52% mated and 48% virgin females was found. Therefore, the pheromone together with the odour of rotting coconut stems signals a reproduction site to beetles, particularly mature females. In practice, the pheromone-baited traps will help in reducing the dissemination of gravid females, but will not affect directly the numbers of immature ones attacking palms. Our results show that when using pheromones for monitoring or controlling insects, the physiological status of the insects may have unexpected effects on the outcome.     

Reproductive behaviour of the South American fruit fly Anastrepha fraterculus (Diptera: Tephritidae): laboratory and field studies

Abstract. The mate choice, courtship and oviposition behaviour of laboratory-reared and field-collected Anastrepha fraterculus (Wied.) were compared. In laboratory cultures in Southampton the duration of male calling activity in small leks increased gradually from 1-2h at 5 days old to up to 7 h at 10 days. This finding correlates with previous reports on the time at which male salivary glands, which are believed to produce sex pheromone, are fully developed. Wild flies which emerged from infested fruits in Brazil began to oviposit on the day they mated, whereas in laboratory flies oviposition began 1 day following the first mating. Both types of fly usually defended their position on a particular fruit throughout the day, and re-mated with either virgin or mated males. There was no significant difference in mating duration. Females did not copulate before the mean age (±SE) of 16.8±0.9 days. For both types of flies mating initiation occurred in the first 2h of photophase, with virgin females choosing mainly mated males. The average number of matings in the laboratory was three for females and four for males, and the interval between matings in females was significantly increased after the second mating. It is suggested that the tendency of virgin females to mate with mated males will lead to increased fitness, as males are on average 48 days old at their second mating. The potential life span of around 200 days for both sexes would allow adults to bridge the gap between seasonally available fruits in warm-temperate and sub-tropical South America.     

The length of the fertility period of the rat spermatozoa]

4-day cyclic Wistar female rats were caged with sexually experiences males at either 18:00-19:00 on proestrus or at 21:30-22:30 during the following night. 16 out of 17 bulbectomized females and 16 out of 40 intact females respectively mated at 18:00-1900. 22 out of 24 intact females mated at 21:30-22:30. Only 11 out of the 32 receptive females became pregnant in the first group while 14 out of the 22 receptive females went into pregnancy in the second group. It is then supposed, given that ovulation does not take place before midnight during the night from proestrus to estrus in the rat that the fertilizing capacity of spermatozoon is of relatively short duration in the rat.     

The effect of enforced virginity and subsequent mating on the activity of the corpus allatum of Periplaneta americana measured in vitro, as related to changes in the rate of ovarian maturation

ABSTRACT. Female P. americana, reared with males from the time of adult emergence, mated on the 4th–5th day after metamorphosis, produced the first ootheca on the 8th or 9th day, and then produced successive oothecae at intervals of 3.0 days, whereas, only 50% of virgin females had produced their first ootheca by the 28th day after adult emergence. Examination of the ovaries indicated that oocyte development is normal in virgins until shortly after the time when they first become receptive to males. When mating was not allowed there was a dramatic reduction in the rate of vitellogenic growth of the terminal batch of oocytes which persisted until mating was allowed, and was often accompanied by resorption of a percentage of the oocytes. Short-term, in vitro, radiochemical assay of juvenile hormone (JH III) biosynthesis by corpora allata (CA) showed that, in females reared with males, the cycles of ovarian development are accompanied by regular pulses of CA activity. There is a small, possibly preparatory peak of JH III biosynthesis before vitellogenesis of the first wave of oocytes, followed by a larger peak of JH III production during vitellogenesis of this batch of eggs and one peak of CA activity between ovulation of each subsequent wave of oocytes. Activities as low as 0.25 pmol C₁₆JH/CA pair/h and as high as 48.38 pmol/CA pair/h were observed in CA from mated females after the onset of cyclic activity. Stimuli received during mating are somehow responsible for the cyclic activity of the CA, for when females were subjected to enforced virginity the first small peak was normal but the second peak was not fully realized and there was then a gradual decline in CA activity until approximately 2 weeks post-emergence. Thereafter the glands exhibited a more or less constant rate of JH biosynthesis (mean = 3.45 ± 0.32 pmol/CA pair/h.) When females were mated after 21 days of enforced virginity the activity of the CA was enhanced. By 48 h after mating the mean glandular activity was at least four times that found in virgins of the same age, and by 72 h rates as high as 40 pmol/CA pair/h were observed. This was followed by normal cyclic activity of the CA. The increase in rate of JH biosynthesis appears to result in a recommencement of oocyte development in these ‘delayed-mated’ females.     

Reproductive and developmental biology of the oriental cockroach Blatta orientalis (Dictyoptera)

At 27 degrees C and 45% r.h. in the laboratory, the oriental cockroach Blatta orientalis (L.) developed to adulthood in seven to nine instars for males (66% had eight instars) and eight to ten instars for females (67% had nine instars) in mixed groups, with up to twelve instars for isolated females. Nymphal development lasted 185 +/- 2 days for males, 216 +/- 4 days for females, with 89% survival to adulthood. Adult longevity was significantly more for males than females in mixed groups. Virgin females lived for 135 +/- 6 days compared with 87 +/- 9 days for females kept with males. After an initial maturation time of 12.2-13.5 +/- 0.4 days for mated and unmated females, oothecae were produced, on average, every 6-7 (range 2-29) days. Ootheca viability was 68% from females kept with males, 32% from females kept apart from males. Numbers of nymphs emerging were 14.1 +/- 0.26 after 45 days from mated female oothecae 8.2 +/- 0.3 after 49 days from unmated females. With sexual reproduction the sex ratio of progeny reaching adulthood was 1.1 males per female (n = 443), whereas unmated females produced only female progency, which is consistent with parthenogenetic reproduction. Drawings of the ventral aspect of the terminalia are given to show features useful for instar determination and for distinguishing between male and female nymphs and adults of B. orientalis.     

Patterns of sexual receptivity in the female musk shrew (Suncus murinus)

Female musk shrews (Suncus murinus) were tested daily to examine patterns of sexual receptivity. When only mounting was used as a criterion (to avoid pregnancy), nonpregnant females remained sexually receptive to males every day for 14 consecutive days. When insemination was allowed, most females continued to copulate for the first 5 days of pregnancy. Receptivity declined markedly around Day 10 of gestation, but a few females were receptive even into late pregnancy. Lactating females copulated with males 5 and 10 days after parturition. In general, unlike most mammals studied in the laboratory, the nonpregnant female musk shrew has no behavioral estrous cycle. Musk shrews are ready to mate anytime except in mild to late pregnancy, and even then occasionally mating is found.     

Male adaptations to minimize sexual cannibalism during reproduction in the funnel‐web spider Hololena curta

Males of many spider species risk being attacked and cannibalized while searching for, courting, and mating with conspecific females. However, there are exceptions. We show that the funnel‐web spider, Hololena curta, has 3 adaptations that minimize risk to males during courtship and mating, and enhance reproductive success. First, males detected chemical or tactile signals associated with webs of virgin females, and differentiated them from webs of mated females, enabling males to increase encounter rates with virgin females and avoid aggressive mated females. Second, males produced stereotyped vibrational signals during courting which induced female quiescence and suppressed female aggression. Third, when touched by males, sexually receptive females entered a cataleptic state, allowing males to safely approach and copulate. Because males can mate multiple times and the sex ratio in natural populations of H. curta is female biased, overall reproductive output is likely increased by males of this species avoiding sexual cannibalism.     

Courtship and male discrimination between virgin and mated females in the orange tip butterfly Anthocharis cardamines

Recent evidence implies that male butterflies incur non-trivial costs in producing ejaculate, and that the number of ejaculates they can produce is limited. Therefore males should be expected to show some mate discrimination. In butterflies, the reproductive value of females, by necessity, decreases with age and, therefore, males should be expected to court young virgin females more intensively than old mated females. In the orange tip butterfly, Anthocharis cardamines, we show that males exhibit behaviour consonant with this hypothesis. They court unreceptive virgin females for approximately 60 s before giving up, whereas unreceptive mated females are courted for only about 3 s before the male departs. We also show that receptive virgin females usually detain courting males by performing an ‘elevated abdomen’ display for about 4 s before accepting the male, and that this display is identical in form to that used by mated females to reject courting males.     

Circadian locomotor rhythm masked by the female reproduction cycle in cockroaches

Blattella bisignata (Brunner) and B. germanica (L.) are oviparous cockroaches with cyclic reproductive behaviour, but in B. germanica only males show circadian rhythmicity of locomotion at 28°C and DD (constant darkness). In B. bisignata, males and virgin females cockroaches entrained by light–dark cycles show free‐running rhythmicity in DD, and most activities occur during the subjective night. Daily locomotor activities of virgin females show cyclic changes that coincided with ovarian development. Virgin females also exhibit calling behaviour during the subjective night, and this shows a free‐running rhythm. Male mate‐finding locomotion and female calling behaviour are under circadian control, so the timing for both behaviours is synchronized. However, most mated females do not show a locomotor free‐running rhythm under DD conditions. Our results indicate that only mated females could not express a circadian locomotor rhythm. Pregnancy reduces a female’s locomotory intensity and masks the expression of a circadian locomotor rhythm. We attribute the differences in circadian locomotory rhythms between these two species to their living environments and mate‐finding strategies.     

Calling behavior of the female german cockroach,Blattella germanica (Dictyoptera: Blattellidae)

Virgin German cockroach females, Blattella germanica(L.), were observed, for the first time, to exhibit a characteristic calling behavior during which females emit a volatile sex pheromone. Under a photoperiod of 12L12D, the percentage of 7-day-old virgin females that exhibited this behavior peaked before the end of the scotophase in a similar pattern to the diel periodicity of mating. A clear relationship was evident between calling and stages of sexual receptivity during successive gonotrophic cycles. Females initiated calling 5–6 days after the imaginal molt, when their basal oocytes were 1.6 mm long. If not mated, females continued to exhibit bouts of calling during the next 3–4 days until 24 h before ovulation. Calling was completely suppressed by mating as well as the presence of an egg case in the genital atrium in both virgin and mated gravid females. We suggest that calling and the emission of a volatile sex pheromone serve to attract males from a distance as well as to potentiate responses to contact sex pheromone in aggregations.     

Factors affecting female sexual receptivity in the planthopper, Prokelisia dolus

Abstract. The mating system of Prokelisia dolus Wilson (Homoptera: Delphacidae) was characterized by determining: if males and females multiply mate; when transitions occur in female sexual receptivity, what triggers sexual refractoriness; and what behaviours characterize unreceptive virgins, receptive virgins, and unreceptive mated females. Males copulated with up to six females in less than 1 h, but completely inseminate, on average, only the first four females. Females rarely mated more than once, unless males were depleted of sperm due to previous copulations or if copulation was interrupted (if duration was<2 min). Male and female calling was associated (100% and 91%, respectively) with sexual receptivity and resultant matings. The transition from unreceptive virgin to receptive (calling) mature virgin occurred 48 h posteclosion, and all were mated by day 4. Females that were sexually immature and those completely inseminated did not call. Rejection of males by females included walking away from approaching males (65%), female kicking (7%), and abdominal lifting (5%). Rejection of males was observed by immature, mature and calling, and mated females. Sexual refractoriness was not triggered by acoustic and visual stimuli or mechanical stimulation of genitalia. Refractoriness was also not triggered by reception of small quantities of sperm because some females laid a few viable eggs yet calling was not terminated. Sexual refractoriness was activated by a substance in the ejaculate as demonstrated by injection into the haemocoel of male accessory glands or testes and homogenates of seminal vesicles. This is the first study that documents the role of male ejaculate in inhibiting female sexual receptivity in Hemiptera (Homoptera).     

Reproduction-flight relationship in the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

To evaluate the relationship between reproduction and migratory flight, we examined ovaries, tethered flight, and egg laying in the beet armyworm, Spodoptera exigua (Hübner). Ovarian development in female S. exigua was classified into five stages in relation to the postemergence age of the moths. Oviposition peaked at ovarian stages III and IV. Mating accelerated ovarian development in this species, and thus the mated females developed faster than the virgin moths in ovaries. In virgin adults, flight capacity increased from the first day to the third day after emergence and remained at a high level until the moths were 7 d old. In contrast, the mated moths reached the maximum flight capacity in 2 d after emergence and maintained a high level until the age of 7 d. However, mating status could not influence the flight capacity of the beet armyworm, although there were general differences in flight capacity between virgin and mated adults at the same age. Moreover, significant correlations between the number of eggs laid and the flight capacity were not performed by the mated moths. These results showed that mating status and ovarian development did not seem to influence flight capacity in the beet armyworm, which was not in agreement with the definitions of the oogenesis-flight syndrome observed in many other migratory insects.     

Mating Status Effects on Sexual Response of Males and Females in the Parasitoid Wasp <Emphasis Type="Italic">Urolepis rufipes</Emphasis>

Although mate preferences are most commonly examined in females, they are often found in both sexes. In the parasitoid wasp Urolepis rufipes, both female and male mating status affected certain aspects of sexual interactions. Female mating status mattered only in the later stages of mating. Males did not discriminate between virgin and mated females in terms of which they contacted or mounted first. However, once mounted, most virgin females were receptive to copulation, whereas very few mated females were. Whether a male’s mating status affected his own sexual response depended on the female’s ability to respond and the stage of mating. Examining male behavior toward dead females allowed elimination of the role of female behavior in how males responded. Virgin and mated males are both attracted to dead females as evidenced by their fanning their wings at such females. However, mated males were quicker than virgin males to contact and to mount in an experiment with dead females, whereas there was no such differential response in an experiment with live females. This difference is consistent with greater female sexual responsiveness to virgin males. Male mating status also affected female receptivity to copulate. Once mounted, live virgin females were less likely to become receptive to copulation by mated males than to virgin males, but only in a choice experiment, not in a no-choice experiment.     

The relation of ovarian steroid levels in young female rats to subsequent estrous cyclicity and reproductive function during aging

In multiparous rats, the incidence of regular estrous cyclicity and fertility decreases markedly at middle age. However, recent studies have shown that repeated pregnancies or progesterone (P) implants can subsequently cause retired breeder females to maintain regular cyclicity for an extended period of time; these results suggest a P-mediated deceleration of reproductive aging. In the present study, we examined the relation of ovarian steroid levels in young virgin females to their subsequent estrous cyclicity and reproductive function during aging as compared to multiparous females. Beginning at 4 mo of age and continuing to 6 mo of age, regularly cyclic virgin rats received either consecutive P implants (n = 41) or no implants (controls, n = 45) for 3 wk, followed by implant removal for 1 wk. Additional females (n = 72) were mated and allowed to undergo repeated pregnancies at 4, 6 1/2, and 8 mo of age. Blood samples were obtained throughout the estrous cycle (virgin females), during pregnancy (multiparous rats), and on Day 11 of successive treatments with P implants (virgins with P implants) for P, estradiol (E2), and testosterone (T) measurements. Subsequently, regularly cyclic females from all three groups were mated with fertile males to undergo term pregnancies at 10 and 12 mo of age. While the virgin controls showed cyclic increases in P, T, and E2 secretion during their estrous cycles, the P-implanted females had persistently low E2 and high P and T levels during treatment, which indicates an inhibition of ovarian E2 synthesis by P.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calling behaviour of adult female Helicoverpa armigera (Hübner) (Lep., Noctuidae) of overwintering generation and effects of mating

The calling behaviour of overwintering generation females of Helicoverpa armigera and the effects of mating were studied in the laboratory at 24 ± 1°C and under reversed light-dark cycle (16 h light : 8 h dark). Age had a significant influence on calling patterns. Based on calling age, mean number of calling bouts and total calling length of virgin females increased significantly, and mean onset time of calling advanced significantly from calling day 1 to subsequent calling days. Females of the overwintering generation exhibited more short bouts in calling, and some females that initiated calling on a previous day did not call on subsequent days. Mating had no effect on the overall patterns, but did affect calling behaviour. Mated females did not resume calling after mating during the same scotophase and, on the day following mating, mated females called less frequently and for a shorter duration, but thereafter increased to the same level of virgin females of the same calling age. Furthermore, as the moth aged, the percentage of mated females calling was lower than that of virgin females.