Mate choice in the Polychaete nereis acuminata : the role of aggression and parental experience
Storey, Ellen Julia
Thesis or dissertation
- © 2010 Ellen Julia Storey. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
Nereis acuminata is a polychaete species with a unique life cycle. A male and female form a monogamous pair bond, the female lays eggs and dies. The male then fertilises the egg and undertakes sole parental care until the eggs hatch and larvae leave the parental burrow; the male can then reproduce again. This body of work investigated aggression, pair formation, filial cannibalism, the scent of experience and the occurrence of male parental care for eggs fertilised by another male in the polychaete species Nereis acuminata.Female aggression following egg release was found to be absent when the females were not in the presence of an egg mass, with no aggression displayed towards sexually mature females. Aggression between two males did not have a subsequent effect on the pairing behaviour with a female, although there was slight decrease (not significant) in the time taken for individuals to pair if they had previously formed a pair bond. Males that had previously had an aggressive encounter were fought subsequently to determine if there was recognition for previous opponent but aggression did not change following previous fights, indicating that previous fights between the same opponents does not have an effect on the aggression levels exhibited. Aggression between the populations maintained in the laboratory, Reish (R), Newport (N), San Gabriel (SG), Connecticut (C) and the wild population Los Angeles (LA) were examined. Although there were significant differences in male aggression between the R, N, SG and C populations, and significant differences in female aggression between the R and LA populations, aggressive behaviour was not found to be a strong indicator of population divergence. Observations of pair formation, however, provided a stronger indicator of divergence. Pairing behaviour within each population was found to be significantly different to that between individuals from different populations, with Connecticut individuals failing in the majority of cases to form a pair bond with any of the other three laboratory populations. The LA and R populations, sampled in the same location 44 years apart, did not form pairs with the same frequency as males and females from the same population but interactions between R and LA males and females were found to form a high frequency of pairs, indicating that although the R population may be heavily inbred, females of this population will still form monogamous pairs with males from the LA population. The behavioural and molecular evidence suggests that these populations form a species complex and this is important to note when undertaking ecotoxicology testing as the different populations may respond differently to the same environmental conditions.The occurrence of filial cannibalism was investigated in male N. acuminata, looking at aggressive interactions between males and female mate choice. The presence of a cannibalistic male did not affect the aggression observed between two individuals and it appeared that females could not discriminate between males that had cannibalised their egg mass. Conditioned water was used from various sources to determine if female preference could be altered following an initial selection of male by the female. Water from males caring for eggs and from new experienced males that had just completed egg care was found to change the choice of the female to a pre-treatment loser. Water conditioned from females, juveniles and inexperienced males appeared to enforce the previous choice of the female as in these trials the female chose the previous winner more frequently. The mechanisms related to the scent of experience in terms of physiology and release of the chemical signal however, are still unknown. It is thought that there is a physiological change in the male, for example by release of sperm or by production of ‘new’ sperm that the female can detect and uses to indicate that a male has previously cared for a brood. As the female dies following egg release and the male undertakes sole parental care, an honest indication of the ability of the male to successfully care for eggs is vitally important.Finally, male behaviour towards an egg mass fertilised by another male was investigated. Inexperienced males that had not completed egg care were found to care for the eggs until they hatched whereas experienced males were not, instead cannibalising the egg mass. Inexperienced males were likely to gain from adopting eggs by gaining parental experience and receiving more matings in the future. Experienced males did not gain benefits from caring for unrelated eggs but cannibalising the eggs would benefit the experienced male by providing extra nutrients.Nereis acuminata is an ideal species to use as a model organism to investigate the behavioural and evolutionary processes involved in mate choice, aggression, preference for parental experience and the chemical signalling involved, due to its adaptable life history, short life cycle and ease of maintenance in the laboratory.
- Department of Biological Sciences, The University of Hull
- Hardege, Jörg D.
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