Environmental cues or conspecific attraction as causes for egg mass aggregation in hydrobiosid caddisflies |
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Authors: | Paul Reich Robin Hale Barbara J Downes and Jill Lancaster |
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Institution: | (1) School of Biological Sciences, Monash University, Clayton, VIC, 3800, Australia;(2) Department of Resource Management & Geography, University of Melbourne, 221 Bouverie St, Melbourne, VIC, 3010, Australia;(3) Present address: Department of Sustainability and Environment, Arthur Rylah Institute for Environmental Research, PO Box 137, Heidelberg, VIC, 3084, Australia; |
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Abstract: | The distribution of egg masses throughout the environment can strongly influence the population dynamics of aquatic insects.
Many species lay eggs in aggregations and most eggs will subsequently hatch from only a few locations—knowing how and why
these aggregations arise is therefore needed to understand the population dynamics of these species. The hydrobiosid caddisfly
Ulmerochorema rubiconum lays eggs in large aggregations on the undersides of emergent rocks in streams. Our aim was to test whether females oviposit
in response to conspecific egg masses or the environmental characteristics of rocks by manipulating the number and age of
egg masses initially present on rocks and monitoring the accumulation of new masses. Our first experiment used rocks that
had recently been used for oviposition and initial egg masses encompassed a range of ages; our second used rocks with no history
of oviposition and initial masses of uniform age. Females did not respond to conspecific eggs of any age, as removing initial
egg masses had no impact on the number of new masses laid in either experiment. There was a strong positive relationship between
the number of initial and new masses, regardless of whether initial egg masses were removed, at the scale of whole rocks and
for rock microhabitats. The results suggest that females select oviposition sites based primarily on physical characteristics
of emergent rocks. We demonstrate for the first time that the spatial arrangement of egg masses may be consistent and predictable
through time, with females showing a high degree of fidelity for particular rocks and microhabitats. |
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