Mating system and alternative male mating tactics in the grass goby Zosterisessor ophiocephalus (Teleostei: Gobiidae) |
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Authors: | C Mazzoldi M Scaggiante E Ambrosin M B Rasotto |
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Institution: | (1) Dipartimento di Biologia, Università di Padova, Viale G. Colombo 3, 35131 Padova, Italy e-mail: rasotto@civ.bio.unipd.it Tel.: +39-49-8276191; Fax: +39-49-8276199, IT |
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Abstract: | Peculiar fertilization dynamics, with males releasing sperm in mucous trails lasting several hours, characterize some demersal
spawning fish. The mating system was investigated in a natural population of one of these species: the grass goby Zosterisessor ophiocephalus (Pallas, 1814), a large coastal goby inhabiting seagrass meadows in shallow brackish water. Adult males ranged in size from
7.4 to 23 cm total length, but only larger ones were observed to dig and defend a burrow, where they performed parental care
on eggs laid by one to several females. Field observations together with analyses of age, sperm production, trail sperm content
and sperm competition tests indicated the occurrence of alternative male mating tactics, likely the expression of an ontogenetic
gradient. Larger males are older than smaller ones, and while the former are territorial, the latter “sneak” territorial male
spawns. The ejaculate characteristics indicate that grass goby males have functionally polymorphic spawns: in fact sperm trails
of larger males last longer and release fewer sperm than those of smaller males. Sperm production over several days is more
constant in larger than in smaller males, but the total number of sperm released is higher in the latter. The influence of
seminal fluid in the functional intraspecific variability in sperm release in this species is discussed.
Received: 30 December 1999 / Accepted: 31 July 2000 |
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