Decay Of Sexual Traits In Thelytokous Strain Of Trichogramma Dendrolimi

Formerly adaptive traits may become non-functional or maladaptive when environmental shifts and life-history changes happen,and consequently such traits may decay under neutral mutation accumulation or selective processes.In genetics,the vestigialization is considered as a form of regressive evolution,highlighting the importance of species evolution.However,the major challenges for studying the trait decay have been to disentangle neutral from selective process and lack information on the costs of traits and so forth.Regressive evolution of sexual traits in asexual lineages,luckily,can provide insights into both decay via neutral mutation accumulation and selective processes,and occurs in a broad range of taxa.It is therefore a good model to the studies there above.Among which,Wolbachia-induced thelytoky recently has been popular for the relative broad occurrence in Hymenopterans,general sexual controls in nature,bisexual individuals or even lineages that can be obtained by antibiotic or heat treatments,and the studying convenience of haplodiploid species.In current study,we explored the sexual traits decay on thelytokous strain of Trichogramma dendrolimi by investigating the sexual behavior,male fertility,external morphology and antennal sensilla in both bisexual and thelytokous strains of T.dendrolimi.This study is the basis for us to understand the evolution of Wolbachia-induced thelytokous species.The findings of current were listed as follows:1.This study firstly investigated the decay of bisexual behaviors in thelytokous strains.The results showed that bisexual males had a significantly higher courtship frequency to thelytokous females than to bisexual females and the instantaneous risk was also significantly higher;Male wasps presented lower success rate when mated with thelytokous females;significantly longer copulation duration was showed in the mating groups comprising bisexual males and thelytokous females;thelytokous males displayed no significant changes in courtship and mating behaviors,but they exhibited a significantly higher courtship frequency to bisexual females.These results suggested the decay in recognizing mates or their courtship and mating behavior,and the reduction of attraction of thelytokous males to bisexual females.2.On the basis of decay of thelytokous male attraction to bisexual females,we further investigated the male 'fertility' in asexual lineage,i.e.,female fertility,female longevity,female proportion and emergence rate of offspring,that are related to its reduction.The female fecundity,female longevity,female ratio of offspring and female eclosion rate were 40.70±8.56,3.250±0.403,62.083±10.043 and 88.4±2.5%.Female fecundity,female longevity,female offspring ratio and female emergence rate of male bees after mating were 63.05±10.96,2.300±0.339,78.813±9.800 and 88.3±2.1%.Our results suggested no significant changes of fertility of thelytokous males or other related factors.Moreover,the reduced attraction of thelytokous males stemmed from thelytokous females and the reduction was moderate.3.As the decay of traits is often related to the changes of morphology,we also compared the external morphology between two strains.The results showed significantly reduced ovary(Td T-HR: 8605.98±510.72 ?m~2,Td-HR: 12354.48±836.75 ?m~2),spermatheca(Td T-HR: 695.03±67.11 ?m~2,Td-HR: 839.22±38.72 ?m~2)and egg(Td T-HR: 63.03±1.54?m,Td-HR: 71.59±1.84 ?m)in size,but a significant increase of ovipositor(Td T-HR:122.77±5.50 ?m,Td-HR:114.74±3.69 ?m)of thelytokous females than those of bisexual females;for other external morphology,no significant changes were found except in antennal length.The changes of ovary and egg size may be related to the balance of a population in nature.The significant reduction in size of spermatheca suggested the occurrence of its decay by either negative selection or neutral mutation accumulation.The changes of length in ovipositor may involve the horizontal transmission of Wolbachia.As secondary sexual characteristic,the change of antennae may be related to the decay of sexual traits.4.Antennal sensilla of parasitoid wasps play important roles in foraging,mate-seeking,courtship and mating.Therefore corresponding sensilla might decay with the decay of sexual traits.In this study,we investigated the sensilla in both strains,to reveal the relationship between decay of sexual traits in thelytokous strain and the antennal sensilla.We found 15 morphologically distinct types of antennal sensilla and firstly systematized the demonization of sensilla in T.Trichogramma.Sensilla TS1-3,Ch S1-2,St S1-2,PS1-2,Ca S,FS,AS,B?hm distribute in both two strains,but TS4,Ch S3 only presented in thelytokous strain.7 ASs on GSTd and 8 on TSTd,the difference is on second funicle(1 on Td-HR,2 on TdT-HR).No decay of sensilla was found in thelytokous individuals and this may be the consequence of moderate decay of sexual traits.