57
Y. Sadovy de Mitcheson and P.L. Colin (eds.), Reef Fish Spawning Aggregations:
Biology, Research and Management, Fish & Fisheries Series 35,
DOI 10.1007/978-94-007-1980-4_3, © Springer Science+Business Media B.V. 2012
Abstract Animals breed in groups either through necessity, when reproduction
depends on a spatially limited resource, or by choice, when group-breeding conveys
adaptive benefi t to adults or their young. We review evidence for both hypotheses
from a variety of animal taxa before turning our attention to potential explanations
for fi sh spawning in aggregations. Spawning in aggregations may increase reproductive output by increasing mate-encounter rates, facilitating mate choice and/or
improving fertilisation success. Aggregating to spawn may also dilute predation
rates on adults and eggs. However, spawning in aggregations may also carry costs,
such as increased conspicuousness to predators, predator-mediated behavioural
changes, and increased exposure to parasites or diseases. It is also possible that
spawning aggregations occur around specifi c, spatially rare features or resources
that offer a benefi t to spawning fi sh, irrespective of group size. Although explicit
tests of most of these costs and benefi ts have yet to be conducted, existing evidence
indicates that there is unlikely to be a single explanation for why fi sh spawn in
aggregations. Additionally, spawning aggregations present a specifi c and unusual
arena for sexual selection, which shapes the evolution of behaviours and life histories
in group-breeding species. Consequently, elucidating the evolutionary correlates of
aggregation-spawning would be a rich avenue for future research. This chapter explores
the costs and benefi ts of aggregating to breed in a range of fi sh and non-fi sh taxa.
P. P. Molloy (*)
Project Seahorse, Fisheries Centre , University of British Columbia , Vancouver,
BC V6T 1ZA , Canada
Department of Biological Sciences , Simon Fraser University , Burnaby,
BC V5A 1S6 , Canada
e-mail: Philip_p_molloy@gmail.com
I. M. Côté • J. D. Reynolds
Department of Biological Sciences , Simon Fraser University , Burnaby ,
BC V5A 1S6 , Canada
e-mail: imcote@sfu.ca; reynolds@sfu.ca
Chapter 3
Why Spawn in Aggregations?
Philip Patrick Molloy , Isabelle M. Côté , and John D. Reynolds
Y. Sadovy de Mitcheson and P.L. Colin (eds.), Reef Fish Spawning Aggregations:
Biology, Research and Management, Fish & Fisheries Series 35,
DOI 10.1007/978-94-007-1980-4_3, © Springer Science+Business Media B.V. 2012
Abstract Animals breed in groups either through necessity, when reproduction
depends on a spatially limited resource, or by choice, when group-breeding conveys
adaptive benefi t to adults or their young. We review evidence for both hypotheses
from a variety of animal taxa before turning our attention to potential explanations
for fi sh spawning in aggregations. Spawning in aggregations may increase reproductive output by increasing mate-encounter rates, facilitating mate choice and/or
improving fertilisation success. Aggregating to spawn may also dilute predation
rates on adults and eggs. However, spawning in aggregations may also carry costs,
such as increased conspicuousness to predators, predator-mediated behavioural
changes, and increased exposure to parasites or diseases. It is also possible that
spawning aggregations occur around specifi c, spatially rare features or resources
that offer a benefi t to spawning fi sh, irrespective of group size. Although explicit
tests of most of these costs and benefi ts have yet to be conducted, existing evidence
indicates that there is unlikely to be a single explanation for why fi sh spawn in
aggregations. Additionally, spawning aggregations present a specifi c and unusual
arena for sexual selection, which shapes the evolution of behaviours and life histories
in group-breeding species. Consequently, elucidating the evolutionary correlates of
aggregation-spawning would be a rich avenue for future research. This chapter explores
the costs and benefi ts of aggregating to breed in a range of fi sh and non-fi sh taxa.
P. P. Molloy (*)
Project Seahorse, Fisheries Centre , University of British Columbia , Vancouver,
BC V6T 1ZA , Canada
Department of Biological Sciences , Simon Fraser University , Burnaby,
BC V5A 1S6 , Canada
e-mail: Philip_p_molloy@gmail.com
I. M. Côté • J. D. Reynolds
Department of Biological Sciences , Simon Fraser University , Burnaby ,
BC V5A 1S6 , Canada
e-mail: imcote@sfu.ca; reynolds@sfu.ca
Chapter 3
Why Spawn in Aggregations?
Philip Patrick Molloy , Isabelle M. Côté , and John D. Reynolds