Male Mating Behavior Research Articles

An androgenic endocrine disruptor alters male mating behavior in the guppy (Poecilia reticulata)

An androgenic endocrine disruptor alters male mating behavior in the guppy (Poecilia reticulata)

Diapause affects cuticular hydrocarbon composition and mating behavior of both sexes in Drosophila montana.

Environmental cues, mainly photoperiod and temperature, are known to control female adult reproductive diapause in several insect species. Diapause enhances female survival during adverse conditions and postpones progeny production to the favorable season. Male diapause (a reversible inability to inseminate receptive females) has been studied much less than female diapause. However, if the males maximized their chances to fertilize females while minimizing their energy expenditure, they would be expected to be in diapause at the same time as females. We investigated Drosophila montana male mating behavior under short-day conditions that induce diapause in females and found the males to be reproductively inactive. We also found that males reared under long-day conditions (reproducing individuals) court reproducing postdiapause females, but not diapausing ones. The diapausing flies of both sexes had more long-chain and less short-chain hydrocarbons on their cuticle than the reproducing ones, which presumably increase their survival under stressful conditions, but at the same time decrease their attractiveness. Our study shows that the mating behavior of females and males is well coordinated during and after overwintering and it also gives support to the dual role of insect cuticular hydrocarbons in adaptation and mate choice.

Female masculinization and reproductive success in Cnesterodon decemmaculatus (Jenyns, 1842) (Cyprinodontiforme: Poeciliidae) under anthropogenic impact.

Aquatic organisms are exposed to a myriad of chemical compounds, with particular concerns focused on endocrine disruptors. Growing scientific evidence indicates that these compounds interfere with normal endocrine function and could affect the reproductive system of humans and wildlife. We analyzed the proportion of masculinized females, defined by elongation and fusion of the anal fin rays, and the extent of masculinization, masculinization index, defined by anal fin length divided by the standard length, of Cnesterodon decemmaculatus resident to areas of agricultural and urban-industrial activities in the Arroyo Colorado basin. Additionally, a bioassay was carried out to assess the potential effects of masculinization on reproductive success, measured as the number of viable progenies, using pregnant females from the site downstream of the urban-industrial zone. Masculinized females were observed in all sampling sites, particularly downstream of the urban-industrial area, where over 80% of females presented abnormal sexual characteristics and the highest masculinization index was registered. In the laboratory, masculinized adult females showed male mating behavior, and survival of their progeny was lower than those of normal females. To our knowledge, this is the first report of endocrine disruption in field-collected C. decemmaculatus, and the first evaluation of the reproductive success of masculinized females. Finally, our results support C. decemmaculatus as an excellent sentinel species due to its wide distribution, easy culture in laboratory conditions, and its potential capability to respond to sources of pollution, particularly endocrine disruptors.

A case of behavioural diversification in male floral function \u2013 the evolution of thigmonastic pollen presentation

Obvious movements of plant organs have fascinated scientists for a long time. They have been studied extensively, but few behavioural studies to date have dealt with them, and hardly anything is known about their evolution. Here, we present a large experimental dataset on the stamen movement patterns found in the Loasaceae subfam. Loasoideae (Cornales). An evolutionary transition from autonomous-only to a combination of autonomous and thigmonastic stamen movement with increased complexity was experimentally demonstrated. We compare the stamen movement patterns with extensive pollinator observations and discuss it in the context of male mating behavior. Thigmonastic pollen presentation via stamen movements appears to be a crucial component of floral adaptation to pollinator behaviour, evolving in concert with complex adjustments of flower signal, reward and morphology. We hypothesize that rapid adjustments of pollen presentation timing may play a significant role in the diversification of this plant group, representing a striking example for the evolutionary significance of plant behaviour.

Identification and functional analysis of the doublesex gene in the sexual development of a hemimetabolous insect, the brown planthopper

In the sex determination cascade, the genes dsx (doublesex) in insects, mab-3 (male abnormal 3) in nematodes, and Dmrt1 (dsx/mab-3 related transcription factor-1) in vertebrates act as the base molecular switches and play important roles. Moreover, these genes share the same conserved feature domain-DNA-binding oligomerization domain (OD1), and female-specific dsx also has a conserved oligomerization domain 2 (OD2). Although sex determination and the functions of dsx in several holometabolous insects have been well documented, sex determination and the function of dsx in hemimetabolous insects remain a mystery. In this study, four dsx homologs were unexpectedly found in the Nilaparvata lugens (brown planthopper, BPH, order Hemiptera), which also showed a different evolutionary status. We found that only one of the four homologs, Nldsx, which has three alternative splicing variants (female-specific NldsxF, male-specific NldsxM, non–sex-specific NldsxC), was required in the sexual development of N. lugens. Compared with that of holometabolous species, the dsx of N. lugens contains a less conserved OD1, while the OD2 domain of BPH was not identifiable because the common region is poorly conserved, and the female-specific region is short. RNAi-mediated knockdown of Nldsx in female BPH resulted in a larger body size with a normal abdomen and reproductive system, while no changes in fertility were noted. However, adult males with RNA interference knockdown of NldsxM in nymphs became pseudofemales, were infertile, had abnormal copulatory organs, and had impassable deferent ducts with hyperplastic walls; additionally, the pseudofemales could not produce the normal courtship signals. Our results suggest that dsx plays a critical role in male BPH somatic development and mating behavior. This is the first study to show that dsx is essential for sexual development in a hemipteran species.

Courtship diverges with foraging behaviour in artificially selected populations

The sensory drive hypothesis proposes that natural selection on certain behaviours will alter sensory system properties and result in correlated evolution of unrelated behaviours reliant on that sensory system. Here, we used artificially selected populations to demonstrate that selection on colour-based foraging behaviour is associated with divergence of male sexual display behaviour. In a previous experiment, populations of guppies, Poecilia reticulata, were selected for increased chase behaviour towards a red or a blue prey item. In this study, we conducted behavioural trials using these artificially selected populations to show that male mating behaviour diverged after artificial selection on foraging behaviour. The behavioural trials showed that the number of courtship displays and total mating activity were reduced in populations selected to chase a red prey item compared to control populations and populations selected to chase a blue prey item. These results show that artificial selection for a given behaviour can result in changes in unrelated behaviours. Our study has shown that selection on a nonmating behaviour may have consequences for sexual behaviour and the evolution of sexual signalling that has previously not been considered.

Sexual dimorphism in visual and olfactory brain centers in the perfume-collecting orchid bee Euglossa dilemma (Hymenoptera, Apidae).

Insect mating behavior is controlled by a diverse array of sex‐specific traits and strategies that evolved to maximize mating success. Orchid bees exhibit a unique suite of perfume‐mediated mating behaviors. Male bees collect volatile compounds from their environment to concoct species‐specific perfume mixtures that are presumably used to attract conspecific females. Despite a growing understanding of the ecology and evolution of chemical signaling in orchid bees, many aspects of the functional adaptations involved, in particular regarding sensory systems, remain unknown. Here we investigated male and female brain morphology in the common orchid bee Euglossa dilemma Bembé & Eltz. Males exhibited increased relative volumes of the Medulla, a visual brain region, which correlated with larger compound eye size (area). While the overall volume of olfactory brain regions was similar between sexes, the antennal lobes exhibited several sex‐specific structures including one male‐specific macroglomerulus. These findings reveal sexual dimorphism in both the visual and the olfactory system of orchid bees. It highlights the tendency of an increased investment in the male visual system similar to that observed in other bee lineages, and suggests that visual input may play a more important role in orchid bee male mating behavior than previously thought. Furthermore, our results suggest that the evolution of perfume communication in orchid bees did not involve drastic changes in olfactory brain morphology compared to other bee lineages.

Male mate preference as an agent of fecundity selection in a polymorphic salamander.

Color polymorphisms are associated with variation in other traits which may affect individual fitness, and these color‐trait associations are expected to contribute to nonrandom mating in polymorphic species. The red‐backed salamander (Plethodon cinereus) exhibits a polymorphism in dorsal pattern: striped and unstriped, and previous studies have suggested that they may mate nonrandomly. However, the mechanism(s) contributing to this behavior remain unclear. Here we consider the role that male preference may have in driving mating behavior in P. cinereus. We limit our focus to striped individuals because this morph is most likely to be choosy given their dominant, aggressive behavioral profiles relative to unstriped males. Specifically, we evaluated (a) whether striped males preferentially associate with females with respect to her dorsum color, size, and body condition and (b) if so, whether female traits are evaluated via visual or chemical cues. We also considered whether the frequency of another male social behavior, nose taps, was associated with mate preferences. We found that striped male P. cinereus nose tapped more often to preferred females. However, males only assessed potential mates via chemical cues, preferring larger females overall. Reproductive phenology data on a sample of gravid females drawn from the same population indicated that the color morphs do not differ in reproductive traits, but larger females have greater fecundity. Given our findings, we conclude that female P. cinereus are under fecundity selection, mediated by male preference. In this manner, male mating behavior contributes to observations of nonrandom mate associations in this population of P. cinereus.

Plant Chemicals and the Sexual Behavior of Male Tephritid Fruit Flies

Plant compounds affect insects in many different ways. In addition to being a food source, plants also contain secondary metabolites that may have positive and negative impacts on insects. The influence of these compounds on sexual behavior, in particular, has been the focus of many recent studies. Here, we review the existing literature on the effects of plant compounds on the sexual behavior of tephritid fruit fly males. We put special focus on polyphagous species whose males congregate in leks, where females exert strong mate selection. We first summarize the main findings related to plant compounds that increase male signaling behavior and attraction of females and consequently increase mating frequency, a phenomenon that has been recorded mainly for species of Anastrepha and Ceratitis. In other tephritid species, males are attracted to phenylpropanoids produced by plants (such as methyl eugenol or raspberry ketone) that, upon encounter, are consumed and sequestered by males. These compounds, or metabolic derivatives, which normally have negligible nutritional value, are included in the pheromone and also confer advantages in a sexual context: enhanced female attraction and improved male mating success. These phenomena have been reported for several Bactrocera species as well as for Zeugodacus cucurbitae. Because many tephritid species are serious pests, the effect of plant compounds on male behavior has been explored for potential incorporation into control strategies such as the sterile insect technique (SIT). We conclude noting several factors, such as age and nutrition during larval and adult stage, that modulate the effect of plant compounds on male mating behavior as well as some prominent gaps that preclude a thorough understanding of the plant-mediated enhancement of male sexual performance and hence limit our ability to effectively utilize phytochemicals in pest control strategies.

Male morphotypes and alternative mating tactics in freshwater prawns of the genus Macrobrachium: a review

AbstractThe discontinuous variation in male mating behaviour is termed alternative mating tactics. A distinction is commonly made between alternative mating tactics that are fixed for life or flexible with simultaneous or sequential switches between tactics over the sexually mature life. Freshwater species of the genus Macrobrachium demonstrate flexible tactics with sequential (i.e. developmental) switch between tactics. Sexually mature populations of the commercially important giant freshwater prawn M. rosenbergii consist of three morphologically and behaviourally distinct male morphotypes: small males, orange claw and blue claw males, representing (respectively) successive stages in the developmental pathway of sexually mature males. The dominant blue claw males secure mating by guarding receptive soft‐shelled females with their long chelipeds while the subordinate SM use an alternative tactic of sneak mating to fertilize females. Current knowledge of the mating behaviour and reproductive success of these male morphotypes, including male competition over females, female mate choice and the involvement of pheromones, is reviewed. So far, the occurrence of distinct sexually mature male morphotypes has been described in 24 species within the genus Macrobrachium. The prevalence of distinct male morphotypes and alternative mating tactics among Macrobrachium species is discussed in view of the phylogeny of the genus, based on molecular markers. The environmental and genetic determination of the male morphotypes is discussed, as well as the evolution of the developmental alternative mating tactics in the genus Macrobrachium. Possible implications for prawns’ aquaculture and future research are suggested.

An experimental study: Does inbreeding increase the motivation to mate?

Inbreeding is a central topic in evolutionary biology and ecology and is of major concern for the conservation of endangered species. Yet, it remains challenging to comprehend the fitness consequences of inbreeding, because studies typically focus only on short-term effects on inbreeding in the offspring (e.g. survival until independence). However, there is no a priori reason to assume that inbreeding has no more effects in adulthood. Specifically, inbred males should have lower reproductive success than outbred males among other things because of inbreeding depression in attractiveness to females and a reduced lifespan. Such differences in future reproductive value should affect male mating behaviour, such that an inbred male of a given age should be more motivated to seize a current mating opportunity than an outbred male of the same age. We used an inventive experimental set-up that enabled us to assess male behaviour in relation to an apparent mating opportunity while excluding potential confounding effects of female preference. Age-, weight-, and size-matched inbred and outbred male canaries (Serinus canaria) were presented with a female that only one male at a time could access visually via a ‘peephole’ and thus when both males were equally interested in seizing the apparent mating opportunity this would result in contest. We find that inbred males spent more than twice as much time ‘peeping’ at the female than outbred males, suggesting that inbreeding indeed causes different behavioural responses to an apparent mating opportunity. Our study is among the first to highlight that inbreeding affects male mating behaviour, and therewith potentially male-male competition, which should be taken into account in order to understand the full range of inbreeding effects on fitness.

Reproductive performance and mating behavior of the predatory bug, Anthocoris minki Dohrn, 1860 (Hemiptera: Anthocoridae)

Anthocoris minki Dohrn, 1860 (Hemiptera: Anthocoridae) is a potential predator for biological control of the pistachio psyllid, Agonoscena pistaciaeBurckhardt & Lauterer, 1989 (Hemiptera: Psyllidae) in pistachio orchards. This study aimed to examine the impact of mating behavior on the reproductive output of A. minki. The study was conducted under the laboratory conditions in 2015 at Harran University. Males and females of A. minkiused in the experiments were obtained from laboratory-reared population and female mating behavior and fertilization capacity of males were investigated. In the multiple mating, matings made after the first copulation had an adverse effect on egg deposition. Mated females deposited significantly fewer eggs in the presence of males than in their absence. Male fertilization capability was evaluated by enabling a single virgin male to mate sequentially with three virgin females in different intervals between mating events. Regardless of the length of interval between mating events, the number of eggs laid by the first-mated female was significantly greater than the number of eggs laid by the second- or third-mated females. The study suggests that achievement of economic and large-scale rearing of A. minki can be done if the post-mating interactions that negatively influence the female reproduction and longevity are understood and handled appropriately.

Male age is associated with extra-pair paternity, but not with extra-pair mating behaviour

Extra-pair paternity is the result of copulation between a female and a male other than her social partner. In socially monogamous birds, old males are most likely to sire extra-pair offspring. The male manipulation and female choice hypotheses predict that age-specific male mating behaviour could explain this old-over-young male advantage. These hypotheses have been difficult to test because copulations and the individuals involved are hard to observe. Here, we studied the mating behaviour and pairing contexts of captive house sparrows, Passer domesticus. Our set-up mimicked the complex social environment experienced by wild house sparrows. We found that middle-aged males, which would be considered old in natural populations, gained most extra-pair paternity. However, both, female solicitation behaviour and subsequent extra-pair matings were not associated with male age. Further, copulations were more likely when solicited by females than when initiated by males (i.e. unsolicited copulations). Male initiated within-pair copulations were more common than male initiated extra-pair copulations. To conclude, our results did not support either hypothesis regarding age-specific male mating behaviour. Instead, female choice, independent of male age, governed copulation success, especially in an extra-pair context. Post-copulatory mechanisms might determine why older males sire more extra-pair offspring.

Male multiple matings and reproductive success in commodity-adapted strains of Sitophilus oryzae

Multiple matings occur in many species of stored-grain insect pests, such as the rice weevil Sitophilus oryzae (L.), with both female and male mating more than once and with more than one partner. Multiple female mating in S. oryzae increased lifetime fecundity by extending the period of time progeny were produced, but consequences of multiple male mating in S. oryzae were not yet studied although it is likely to increase male fitness by increasing offspring production. Here, the effects of polygynous mating on male mating behavior, success, and fitness were assessed in two strains of S. oryzae, one adapted to barley and another to wheat. Two insect strains were considered because they may differ in response depending on the host grain, which present distinct nutritional value to the insects. Mating by pairs formed between the two strains did not impact mating success, but wheat-adapted females exhibited longer mating duration, which was positively correlated with progeny production. Wheat-adapted males exhibited higher fertility than barley-adapted males. When male multiple matings were considered in successive polygynous matings, late matings led to lower non-cumulative values of progeny production, but higher cumulative performance, and wheat-adapted S. oryzae always performed better. Thus, male fitness and grain losses in wheat are higher than in barley, even when S. oryzae was adapted to the latter.

High fat diet alters Drosophila melanogaster sexual behavior and traits: decreased attractiveness and changes in pheromone profiles

Sexual traits convey information about individual quality to potential mates. Environmental and genetic factors affect sexual trait expression and perception via effects on animal condition and health. High fat diet (HFD) is one environmental factor that adversely affects Drosophila melanogaster health, and its effects on animal health are mediated through conserved metabolic signaling pathways. HFD decreases female attractiveness, resulting in reduced male mating behaviors toward HFD females. HFD also affects the ability of males to judge mate attractiveness and likely alters fly condition and sexual traits to impact mating behavior. Here we show that HFD affects both visual (body size) and non-visual (pheromone profiles) sexual traits, which likely contribute to decreased fly attractiveness. We also demonstrate that adult-specific HFD effects on male mate preference can be rescued by changing metabolic signaling. These results demonstrate that HFD alters Drosophila sexual cues to reflect concurrent effects on condition and that less severe behavioral defects can be reversed by genetic manipulations that rescue fly health. This work expands on current knowledge of the role that metabolic signaling pathways play in linking animal health, sexual traits, and mating behavior, and provides a robust assay in a genetically tractable system to continue examining these processes.

Haploinsufficiency of SIX3 Abolishes Male Reproductive Behavior Through Disrupted Olfactory Development, and Impairs Female Fertility Through Disrupted GnRH Neuron Migration.

Mating behavior in males and females is dependent on olfactory cues processed through both the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). Signaling through the MOE is critical for the initiation of male mating behavior, and the loss of MOE signaling severely compromises this comportment. Here, we demonstrate that dosage of the homeodomain gene Six3 affects the degree of development of MOE but not the VNO. Anomalous MOE development in Six3 heterozygote mice leads to hyposmia, specifically disrupting male mounting behavior by impairing detection of volatile female estrus pheromones. Six3 is highly expressed in the MOE, main olfactory bulb (MOB), and hypothalamus; all regions essential in the proper migration of the gonadotropin-releasing hormone (GnRH) neurons, a key reproductive neuronal population that migrates along olfactory axons from the developing nose into the brain. Interestingly, we find that the reduction in Six3 expression in Six3 heterozygote mice compromises development of the MOE and MOB, resulting in mis-migration of GnRH neurons due to improper olfactory axon targeting. This reduction in the hypothalamic GnRH neuron population, by 45% in adulthood, leads to female subfertility, but does not impact male hormone levels, suggesting that male infertility is not related to GnRH neuron numbers, but exclusively linked to abnormal olfaction. We here determine that Six3 is haploinsufficient for MOE development, GnRH neuron migration, and fertility, and represents a novel candidate gene for Kallmann syndrome, a form of inherited infertility.

The antidepressant fluoxetine alters mechanisms of pre- and post-copulatory sexual selection in the eastern mosquitofish (Gambusia holbrooki)

Contamination of aquatic habitats with pharmaceuticals is a major environmental concern. Recent studies have detected pharmaceutical pollutants in a wide array of ecosystems and organisms, with many of these contaminants being highly resistant to biodegradation and capable of eliciting sub-lethal effects in non-target species. One such pollutant is fluoxetine, a widely prescribed antidepressant, which is frequently detected in surface waters globally and can alter physiology and behaviour in aquatic organisms. Despite this, relatively little is known about the potential for fluoxetine to disrupt mechanisms of sexual selection. Here, we investigate the impacts of 30-day exposure to two environmentally realistic levels of fluoxetine (low and high) on mechanisms of pre- and post-copulatory sexual selection in the eastern mosquitofish (Gambusia holbrooki). We tested 1) male mating behaviour in the absence or presence of a competitor male, and 2) sperm quality and quantity. We found that high-fluoxetine exposure increased male copulatory behaviour in the absence of a competitor, while no effect was detected under male-male competition. Further, fluoxetine exposure at both concentrations increased total sperm count relative to males from the control group, while no significant change in sperm quality was observed. Lastly, low-fluoxetine males showed a significant reduction in condition index (mass relative to length). Our study is the first to show altered mechanisms of both pre- and post-copulatory sexual selection in an aquatic species resulting from environmentally realistic fluoxetine exposure, highlighting the capacity of pharmaceutical pollution to interfere with sensitive reproductive processes in wildlife.

Male guppies compensate for lost time when mating in turbid water

Turbidity (a measure of the cloudiness of water) decreases the visual range of organisms, altering interactions within and between species. For species that visually assess mates, turbidity may affect mating interactions and mate choice. A central question, then, is to what degree organisms plastically adjust mating behaviors to cope with visually altered environments. Here, we investigate the effect of turbidity on the mating behavior of guppies (Poecilia reticulata) in Trinidad, where some streams are increasingly turbid due to upstream rock quarrying. We collected fish from two highly turbid streams (with upstream rock quarries) and two pristine streams (no upstream quarries) in the same drainages. We then observed male mating behaviors with females from the same populations in both turbid and clear assays, recording displays and sneak copulation attempts. Males from turbid streams showed greater individual consistency in mating behaviors. But regardless of provenance, male guppies spent less time associating with females in turbid water overall. When males and females did interact, however, males greatly increased the rate of all mating behaviors in turbid as compared to clear water. Thus, even when lacking a long-term evolutionary history with high turbidity, guppies compensate for lost time when mating in a visually altered environment. Given the global nature of increases in turbidity, understanding behavioral responses to this aquatic anthropogenic change is critical. Here, we investigate the degree to which Trinidadian guppy males in affected areas are able to plastically compensate in turbid water by adjusting mating behaviors. We also test the degree to which previous chronic exposure to turbidity alters this plasticity. In contrast to predictions, we did not find population differences in plasticity; across all populations, however, we found significant plasticity in the guppy mating system in response to anthropogenically increased turbidity. While males spent less time associating with females in turbid water overall, males increased mating effort during periods of association, compensating for lost time in turbid water. We discuss this plasticity and the implications for guppy sexual selection and secondary sexual characteristics such as coloration.

How pre- and postcopulatory sexual selection influence male mating decisions in a promiscuous species

When females mate multiply, male reproductive success depends on both pre- and postcopulatory processes, including female choice and sperm competition. However, these processes can favour different mating tactics in males. Here we used the Trinidadian guppy, Poecilia reticulata, system to understand how this conflict is resolved. We asked whether knowledge of recent female mating history leads males to adjust their mating effort with respect to the time devoted to mating activity, and the frequency and the sequence of mating tactics employed. To do this we quantified male mating behaviour in three competitive scenarios: (1) Single, when a focal male arrives near a single female and remains alone with her; (2) First, when a focal male is joined by a rival male; and (3) Second, when a focal male arrives after a rival male. We hypothesized that males adjust their behaviour based on arrival order. If female sequential mate choice is the main process shaping male mating behaviours (favouring First males in guppies), males should avoid competition and invest most when Single. Alternatively, if last-male sperm precedence is the major driver of decision making, males should invest more in mating attempts in the Second scenario. Greatest investment when First implies an intermediate strategy. We found that order of arrival influenced mating decisions with most mating activity during the First rather than the Single and Second scenarios. This result suggests that both pre- and postcopulatory processes influence mating investment, and that individual males make contingent decisions to maximize both mating and fertilization success.

The genetics of egg retention and fertilization success in Drosophila: One step closer to understanding the transition from facultative to obligate viviparity.

Oviparous, facultative egg retention enables Drosophila females to withhold fertilized eggs in their reproductive tracts until circumstances favor oviposition. The propensity to retain fertilized eggs varies greatly between species, and is correlated with other reproductive traits, such as egg size and ovariole number. While previous studies have described the phenomenon, no study to date has characterized within-species variation or the genetic basis of the trait. Here, we develop a novel microscope-based method for measuring egg retention in Drosophila females and determine the range of phenotypic variation in mated female egg retention in a subset of 91 Drosophila Genetic Reference Panel (DGRP) lines. We inferred the genetic basis of egg retention using a genome-wide association study (GWAS). Further, the scoring of more than 95,000 stained, staged eggs enabled estimates of fertilization success for each line. We found evidence that ovary- and spermathecae-related genes as well as genes affecting olfactory behavior, male mating behavior, male-female attraction and sperm motility may play a crucial role in post-mating physiology. Based on our findings we also propose potential evolutionary routes toward obligate viviparity. In particular, we propose that the loss of fecundity incurred by viviparity could be offset by benefits arising from enhanced mate discrimination, resource specialization, or modified egg morphology.