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SPERM COMPETITIVE ABILITY EVOLVES IN RESPONSE TO EXPERIMENTAL ALTERATION OF OPERATIONAL SEX RATIO
Author(s) -
Nandy Bodhisatta,
Chakraborty Pratip,
Gupta Vanika,
Ali Syed Zeeshan,
Prasad Nagaraj Guru
Publication year - 2013
Publication title -
evolution
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.84
H-Index - 199
eISSN - 1558-5646
pISSN - 0014-3820
DOI - 10.1111/evo.12076
Subject(s) - biology , sperm competition , sperm , experimental evolution , competition (biology) , operational sex ratio , sexual selection , sex ratio , selection (genetic algorithm) , zoology , mating , evolutionary biology , ecology , genetics , demography , mating system , population , artificial intelligence , sociology , gene , computer science
In naturally polygamous organisms such as Drosophila , sperm competitive ability is one of the most important components of male fitness and is expected to evolve in response to varying degrees of male–male competition. Several studies have documented the existence of ample genetic variation in sperm competitive ability of males. However, many experimental evolution studies have found sperm competitive ability to be unresponsive to selection. Even direct selection for increased sperm competitive ability has failed to yield any measurable changes. Here we report the evolution of sperm competitive ability (sperm defense‐P1, offense‐P2) in a set of replicate populations of Drosophila melanogaster subjected to altered levels of male–male competition (generated by varying the operational sex ratio) for 55–60 generations. Males from populations with female‐biased operational sex ratio evolved reduced P1 and P2, without any measurable change in the male reproductive behavior. Males in the male‐biased regime evolved increased P1, but there was no significant change in P2. Increase in P1 was associated with an increase in copulation duration, possibly indicating greater ejaculate investment by these males. This study is one of the few to provide empirical evidence for the evolution of sperm competitive ability of males under different levels of male–male competition.