Inviable egg production in Theridion rufipes (Araneae, Theridiidae): a harvest for first instar spiderlings

Downes, Michael Frank (1985) Inviable egg production in Theridion rufipes (Araneae, Theridiidae): a harvest for first instar spiderlings. Masters (Research) thesis, James Cook University.

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Most of the variability in fecundity and fertility in Theridion rufipes is due to differences between individual females. Food availability is the most influential extrinsic factor controlling fecundity and fertility, and the type of food consumed may also have an effect. Fecundity increases in the later egg sacs of the egg sac sequence.

Neither variations in fixed laboratory temperatures nor variations in prevailing field temperatures affect fecundity or fertility, but both development rate and oviposition intervals are markedly influenced by temperature. At a constant temperature of 20° C, development is halted and oviposition interval is greatly extended. At 25° C and 30° C, development proceeds normally and there is no significant difference in mean oviposition interval.

Some differences exist between the two relatively isolated subpopulations of T. rufipes from which experimental specimens were obtained.

The eggs vary in diameter from 0.55 mm to 0.80 mm, the smaller eggs being less likely to develop. The undeveloped eggs are used as a food resource by the first instar spiderlings before they leave the egg sac and disperse. This extra nourishment enables spiderlings to survive without feeding again for up to four times as long as they can without such benefit, enhancing their survival prospects during the dispersal and habitat-selection phase. Many spiderlings that feed on eggs prior to emergence are able to molt to second instar without further nourishment; the size increase resulting from the molt may widen the available prey spectrum.

The mean proportion of inviable eggs in an egg sac is 0.21 (s.e. = 0.01). These values indicate a marked tendency to provide an amount of extra food-egg yolk material that would approximately double the starvation resistance time during the dispersal and settlement phase. It may be impossible or less efficient to provide an appropriate equivalent amount of extra yolk in each egg at oviposition.

Egg-feeding does not occur in the postembryo stage. An account is given of postembryonic development and a proposal is made for standardization of the terms describing araneid early development stages.

Item ID: 15508
Item Type: Thesis (Masters (Research))
Keywords: spiders, Theridiidae, Theridion rufipes, egg production, inviable eggs, fertility, fecundity, spiderlings, juveniles, survival, food availability, feeding, oophagy, oviposition intervals, temperature, egg size, development
Date Deposited: 03 Mar 2011 03:30
FoR Codes: 06 BIOLOGICAL SCIENCES > 0608 Zoology > 060808 Invertebrate Biology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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