Heritability And Evolvability On Thermal Tolerance Traits In Invasive Bemisia Tabaci (Hemiptera: Aleyrodidae) Mediterranean Cryptic Species

With advancing global change, analysis of thermal tolerance and evolutionary potential areimportant to explain ecological adaptation and the changes in the distribution of species.Thermaltolerance is an important factor in the distribution and range dynamics in insects. Thermal tolerancehave received much attention because their investigation provides new insight into the manner in whichclimate shapes variation in the ecology, distribution, hereditary variation and evolution of species. Theinvasive whitefly B. tabaci Mediterranean cryptic species, which is an important invasive pest that isspreading from Mediterranean regions in1993, and is now widely distributed across China except Tibetand Gansu province, ranging from Yangtze River basin to east coastal area even the northest of China,with the trend to replace the native species and MEAM1cryptic species. Higher thermal tolerance wasone of the factors during the invasion and rapid expand for MED cryptic species. To reveal the variationof heat resistance and evolutionary potential in the invasive Bemisia tabaci Mediterranean crypticspecies, we selected four Chinese populations, from Harbin, N China, and Turpan, S China, Beijing MChina and Hainan W China, and conducted knockdown test under static high and low temperatureconditions. Estimate of heritability and genetic variation were based on Parent-offspring design andhalf-sibling breeding design. The main research contents and conclusions are as follows:(1) According to the current status of invasive whitefly B. tabaci Mediterranean cryptic species inour country, we chose four populations collected from different climate regions, including Harbin,northest Heilongjiang province, Haikou, southest Hainan province, Turpan, northwest Xinjiang provinceand Beijing. The field populations of MED were collected from the above regions in July, August andSeptember2012, in which MED occoured in filed at the same time in all the four regions, and then thecorresponding experimental populations were established. Knockdown test were conducted under statichigh temperature conditions. T-test results showed that there were significant differences amongdifferent populations. The heat tolerance of southern population was higher than the three northernpopulations. Heat tolercance between male and female adults of B. tabaci MED were significantdifferent.(2) Knockdown test were conducted under static low temperature conditions. ANOVA showed thatthere were significant differences among different populations on chill coma revoery time. The coldtolerance of southern population was lower than the three northern populations. Cold tolercancebetween male and female adults of B. tabaci MED were significant different both in Harbin and Beijingpopulations, but in Turpan and Haikou populations.(3) Hybrid experimental design were conducted between Heilongjiang and Xinjiang populations asthe average daily temperature and daily maximum temperature trend was similar in the two regions.Knockdown test were conducted under static high temperature conditions on parents, F1and backcrossB1, B2generations. Genetic parameters were estimated from the three generations design. Sex,generation (parents or offspring) and locations were added as fixed factors into this analysis using animal models with restricted maximum-likelihood, which facilitates analyses of unbalanced data setsand the inclusion of fixed effects. Animal models were implemented using REML method based onModelⅠand ModelⅡseperately. The phenotypic (VP) and additive (VA) variance in knockdownresistance were computed using all known relationships among individuals. We carried out Student’st-tests to determine whether variance components and heritability estimates differed significantly.Estimates of evolvability, the additive genetic coefficient of variance,100x(where x isthe sample mean), were computed as well. The narrow sense heritability (h2n) estimates of heattolerance based on parents-offspring regressions ranged from0.45to0.49. The additive geneticcoefficients of variation (CVA) concerning heat tolerance were higher than other speices. The narrowsense heritability (h2n) of heat tolerance traits and high CVAvalue of knockdown time showed thatnatural B. tabaci Mediterranean exhibited high adaptive potential for heat tolerance. Likelihood ratioindicated that ModelⅠwas more suitable for estimating genetic parameters of thermal resistant traits inthis case.(4) Knockdown test were conducted under static low temperature conditions on parents, F1andbackcross B1, B2generations between Heilongjiang and Xinjiang populations. Genetic parameters wereestimated from the three generations design. Sex, generation (parents or offspring) and locations wereadded as fixed factors into this analysis using animal models with restricted maximum-likelihood,which facilitates analyses of unbalanced data sets and the inclusion of fixed effects. Animal modelswere implemented using REML. The narrow sense heritability (h2n) of cold tolerance traits and highCVAvalue of knockdown time showed that natural B. tabaci Mediterranean exhibited high adaptivepotential for cold tolerance.(5) Artificial selection test were conducted in both Heilongjiang and Xinjiang populations under amoderate high temperature of31℃and a moderate low temperature of21℃to survey the varience andtrends of heat tolerance. The results showed that heat resistance were significantly improved bymoderate high temperatures selection after15generations in both Heilongjiang and Xinjiangpopulations compared to the control (26℃). Heat resistance were weakened at G6generations bymoderate low temperatures, but went up then in the following generations in both Heilongjiang andXinjiang populations compared to the control (26℃).(6) Knockdown test were conducted under static low temperature conditions in every threegenerations. Artificial selection were conducted in both Heilongjiang and Xinjiang populations under amoderate high temperature of31℃and a moderate low temperature of21℃to survey varience andtrends of heat tolerance. The results showed that cold resistance were significantly improved bymoderate low temperatures selection after15generations in both Heilongjiang and Xinjiang populationscompared to the control (26℃). Cold resistance were weakened after15generations moderate hightemperatures selection in both Heilongjiang and Xinjiang populations compared to the control (26℃).