Abstract
Abstract. Developmental and growth rates are known to vary in response to genetic, developmental, physiological and environmental factors. However, developmental variations that exist within a cohort under any constant rearing condition are not so well investigated. A few such prominent polymorphisms have been studied, but not the subtle ones. The current study investigates the presence of such varying rates of development, slow and fast, in a cohort reared under constant conditions in two ladybirds, Cheilomenes sexmaculata and Propylea dissecta. Our results reveal slow and fast developers in the cohorts of each species and the ratio of slow and fast developers was similar. Slow developers showed a female biased sex ratio. The two developmental variants differed significantly in juvenile duration only in the first instar and the pupal stage, though variations in developmental time were observed in all stages. Fecundity was higher in slow developers, but developmental rates did not affect egg viability. The similar ratio in both ladybirds indicates it to be a result of either presence of a constant ratio across species or an effect of the similar rearing environment.
Highlights
Variations in environmental factors, such as diet, temperature, and photoperiod (Ernsting and Issaks, 2000; Davidowitz et al, 2004, 2005; Davidowitz and Nijhout, 2004; Plaistow et al, 2005) and the number of predators (Scriber, 2002; Roder et al, 2008; Chown and Gaston, 2010) are well known regulators of change in developmental rate
Maculinea spp., about 25 % of individuals from a cohort develop in one year and the rest in two years (Thomas et al, 1998; Schonrogge et al, 2000; Nowicki et al, 2005; Witek et al, 2006) with the former known as the annual morph, the latter as the biennial morph and the phenomenon as growth rate polymorphism
Similar incidences of growth rate polymorphism have been reported in predaceous syrphid, Microdon mutabilis (Schonrogge et al, 2000) and salmonid fish (Gross, 1985)
Summary
Variations in environmental factors, such as diet, temperature, and photoperiod (Ernsting and Issaks, 2000; Davidowitz et al, 2004, 2005; Davidowitz and Nijhout, 2004; Plaistow et al, 2005) and the number of predators (Scriber, 2002; Roder et al, 2008; Chown and Gaston, 2010) are well known regulators of change in developmental rate. Nylin and Gotthard, 1998; Gotthard, 2001; Davidowitz et al, 2004; Davidowitz and Nijhout, 2004; Stillwell et al, 2007, 2010; Chown and Gaston, 2010) with results indicating faster development under favourable and slower under unfavourable conditions These variations in developmental and growth rates are considered responsible for the variation in sizes including that of the male being smaller than the female in ectothermic organisms
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