Added: Angelita Lu - Date: 03.10.2021 08:07 - Views: 39593 - Clicks: 1272
In animal societies, social life often generates male mating harassment. How do communal animals manage such conflicts without escalating antagonistic relationships? Despite being widespread and abundant during plagues, its populations are otherwise difficult to access, and its reproductive behaviors in the field are understudied.
We show that female locusts behaviorally overcome the costs of male mating harassment: females occupy separate sites before and after mating. Only females with ripe ovaries arrive at male-biased lekking groups. Hence, substantial social conflicts can be simply managed by behaviors. These findings invite to explore the evolutionary hypotheses behind lekking with a density-dependent plastic species. Male mating harassment may occur when females and males do not have the same mating objectives.
Communal animals need to manage the costs of male mating harassment. Here, we demonstrate how desert locusts in dense populations reduce such conflicts through behaviors. In transient populations of solitarious morphology but gregarious behavior , we found that nongravid females occupied separate sites far from males and were not mating, whereas males aggregated on open ground leks , waiting for gravid females to enter the lekking sites.
Once a male mounted a gravid female, no other males attacked the pair; mating pairs were thereby protected during the vulnerable time of oviposition. In comparison, solitarious locusts displayed a balanced sex ratio in low-density populations, and females mated irrespective of their ovarian state. Our indicate that the mating behaviors of desert locusts are density dependent and that sex-biased behavioral group separation may minimize the costs of male mating harassment and competition. Sexual interaction among group members frequently causes competition and male mating harassment 4.
Males typically attempt to maximize fitness by fertilizing as many females as possible 5. Consequently, females are frequently harassed by males, with severe male—male competition 6. Communal animals need to manage the costs of male mating harassment as well as male—male competition. The operational sex ratio OSR is usually biased toward males because males tend to recover their reproductive state faster than females 7. Male-biased OSRs cause male—male competition, leading to intense sexual coercion of females by males i.
This phenomenon reduces female fitness by increasing the risk of predation 8 and injury 9. Sexual conflicts occur when females and males do not have the same mating objectives 12 , However, this phenomenon generates substantial costs, resulting in the loss of energy, time, and mating chance It may also increase predation risk 12 , which may negatively influence population dynamics Exaggerated arms races may be counterproductive for communal animals.
OSR theory proposes the following simple solution for how animals can resolve these opposing forces: females should live separately from males to prevent male mating harassment In some species, males may form leks i. The evolutionary mechanism explaining these paradoxical lekking behaviors remains controversial 2 , Several competing and nonexclusive models have been proposed by considering various factors including predation risk, habitat fragmentation, resource distribution, and male mating harassment In some cases, males are directly or indirectly evaluated based on their quality by females investing in mate choice 17 , However, information about whether this system has evolved in communal animals is limited, especially for species with density-dependent behaviors.
Here, we explored how the desert locust, Schistocerca gregaria , resolves male mating harassment and male—male competition in the field. This extreme phenotypic plasticity termed phase polyphenism depends on local population density 21 , 22 , and the associated behavioral and physiological traits may change quickly during the life cycle 23 , A behavioral difference is measurable within 1 h and almost completed within 4 h In contrast, other traits such as adult morphometric ratios do not change after adult eclosion.
Thus, solitarious-phase looking adult locusts may behave as typical gregarious locusts [referred to as transient 25 or gregarious-behaving locusts; for an explanation of terms, see Study Animal and Terms Used to Describe Populations ]. For gregarious-behaving locusts, little is known about how nongravid females prevent mating harassment by males. Although the desert locust is a major pest in over 60 countries in Africa and Asia 26 , its mating strategies and management of male mating harassment at the group level remain unclear 19 , During field observations over 9 y in the Sahara Desert of Mauritania, we noticed biased sex ratios of sexually mature groups of desert locusts during the transition from the solitarious to the gregarious phase.
In female-biased groups, most females were single i. Researchers ly reported that sexually mature swarms tend to split after oviposition but frequently re when they migratory flight between successive oviposition cycles Based on these observations and theory, we hypothesized that sexually mature, gregarious-behaving desert locust females and males occupied separate areas depending on the state of ovarian development to prevent male mating harassment and to offset costs of male—male competition in mating with gravid females.
We tested this hypothesis by surveying gregarious-behaving populations of desert locusts in the field and by conducting parallel laboratory experiments. Because mating systems vary depending on population density 28 , we also examined the mating system of solitarious-phase locusts in low-density populations. During field surveys performed in September through December to , characteristics and behavioral measurements of 11 transient and 3 solitarious reproducing populations were collected. Five swarming, gregarious, nonreproducing populations were measured to compare adult morphometrics.
These morphometric analyses indicated that the transient gregarious-behaving populations were formed by originally solitarious adults that grew at a low population density during the nymphal stage SI Appendix , Fig. For solitarious population, sex ratio was balanced for hatchlings However, it substantially varied among the sexually mature transient groups Fig.
These seven male-biased lekking groups contained a higher proportion of mating males and females than the nonlek outside groups Table 1. The other four sites had a female-biased sex ratio, with almost no mating activity, which was consistent with our separation hypothesis. Mating systems of sexually mature, transient gregarious-behaving desert locust adults. A Nongravid females outside a lek. B Males aggregating on the hot ground lek and waiting for incoming gravid females during the day, C by raising their bodies off the ground and orienting the body axis parallel to the sunrays.
D Males approaching an incoming female black arrow and fighting for possession of the female at the onset of pairing. E Mating pairs tended to move to the shade at midday and F to aggregate near leks near dusk. G Group oviposition after dusk. Locust density, sex ratio, and mating activity in lek sites versus other sites of transient gregarious-behaving and solitarious locust populations. According to the OSR theory, nongravid females should remain outside leks whereas gravid females should enter leks. To determine whether this behavior was exhibited by gregarious-behaving females, we first examined the daily ovarian developmental rate i.
By dissection, we then determined the ovarian states of females from lek and nonlek sites. The oocytes grew daily. In comparison, nonmating females outside leks had oocytes of various sizes, which corresponded to oocytes that had been developing for 0 to 4 d Fig. In contrast, neither mating nor single solitarious locusts showed a clear pattern in oocyte size Fig. This result indicates that mating by solitarious-phase females was unrelated to the maturity of their oocysts.
Relationships between mating states and ovarian development of sexually mature transient gregarious-behaving A—D and solitarious desert locust females E—H. A and E Daily terminal oocyte development of group-reared gregarious-behaving A and individually reared solitarious locusts E. Each box plot displays the median value with the ends of the boxes representing the 25th and 75th percentiles and the ends of the lines representing the 10th and 90th percentiles.
Frequency of different sized eggs B and F and length of terminal oocyte or mature eggs in the oviduct of mating pairs C and G or single females i. s in parentheses indicate sample sizes. Gray zones indicate the size of mature eggs. Note that only transient males display lekking behavior, and most mating occurred in leks.
Males in lekking groups aggregated on the ground and remained there during the day Fig. With high midday temperatures, some males sheltered in the shade or perched on vegetation to avoid overheating. When a flying gravid female landed on the ground in the middle of a lek, many males immediately approached Fig. One male eventually mounted and paired with the female. Once a male mounted a female, no other male attacked them, and they began to copulate. Such pairs tended to move to the shade to avoid overheating Fig.
Around dusk, when the temperature dropped, many pairs aggregated, and the females oviposited in a group Fig. To assess mating dynamics in lekking sites, we observed diel changes in the sex ratio, of females and males, and mating activity at four sites Fig. The of females entering leks increased, and the sex ratios were almost equal after dusk Fig. This resulted from a decrease in the of males because the males that could not mate moved to night-roosting plants after dusk Fig.Single blk female for France fit male
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Density-dependent mating behaviors reduce male mating harassment in locusts