Alternative male mating tactics in Gobius niger

Abstract

In the field, parental males of the black goby Gobius niger were always>9 cm L T , showed a conspicuous elongation of the first dorsal fin, and were darkly coloured. Larger parental males did not occupy larger nests or obtain more eggs, suggesting that over a threshold size reproductive success was not correlated with male size. The mating system was polygynous with different egg clutches simultaneously present in a nest. Smaller sexually mature males were observed around and inside nests in which spawning was occurring. These opportunistic males ranged in body size between 6 to 8 cm L T . In contrast to parental males, they did not show an exaggeration of the first dorsal fin and were cryptically coloured, thus resembling small females in their external morphology. Aquarium experiments confirmed that smaller males perform a sneaking behaviour, releasing sperm when parental males spawn. As a consequence, it is possible to define three male types: type I are small, without an elongated dorsal fin and adopt a sneaking mating tactic; type III are large, have a pronounced elongation of the dorsal fin and perform parental behaviour; type II are intermediate both in size and elongation of the first dorsal fin and behave as either as sneakers or, possibly, as parental males according to nest availability and male competition.

From sneaker to parental male: Change of reproductive traits in the black goby, Gobius niger (Teleostei, Gobiidae)

“…In nature, sneaker males may be inhibited from changing tactic by visual, acoustic, and /or chemical signals given by black goby parental males performing aggressive displays, producing sound, and releasing pheromones in situations of malemale competition (Marconato, '80;Mazzoldi and Rasotto, 2002). However, the role of these different signals in male-male competition and female choice deserves further investigation.…”

“…Dominant goby males build nests, attract females, and care for eggs (Breder and Rosen,'66;Thresher,'84), while, in several species, subordinate males sneak into nests, and attempt to fertilise eggs but do not contribute to female attraction, territory defence, or parental care (Magnhagen, '92;Mazzoldi and Rasotto, 2002;Mazzoldi et al, 2000). Males performing different mating tactics differ not only in behaviour but also in age, size, and primary and secondary reproductive traits (Magnhagen, '92;Mazzoldi, '99;Rasotto and Mazzoldi, 2002;Scaggiante et al, '99).…”

Ejaculate of sneaker males is pheromonally inconspicuous in the black goby, Gobius niger (Teleostei, Gobiidae)

“…The following male behaviors, typically performed by spawning males (Marconato, '80;Locatello, 2001;Mazzoldi and Rasotto, 2002), were recorded by observations of 10 min every 30 min, for a total of 3 observations before and 2 after the introduction of the acetate sheet (the first one was performed after 15 min from the introduction): (1) number of ''trailing'' (number Á min À1 )¼genital papilla rubs on the ceiling of the nest, this behavior is associated to the release of sperm trails (Marconato et al,'96); (2) mean duration of ''trailing'' (in sec); (3) number of exits¼number of times male exited from the nest with at least half of his body (number Á min À1 ); (4) number of ''gapings'' (number Á min À1 )¼wide opening of male mouth, this behavior is associated to sound emission (Torricelli and Romani,'86); (5) number of male tail beatings (number Á min À1 ), this behavior is associated both to female stimulation and male-male contests (Marconato,'80); (6) number of bites (number Á min À1 )¼male bites against the female, this behavior is associated with the stimulation of females to lay eggs and, in the presence of competitor males, with male-male contests (Marconato '80;Locatello, 2001); (7) any other distinctive behavior.…”

“…Males and females were recognized by the sexually dimorphic genital papilla (Gandolfi et al,'91), measured (total length, TL, to the nearest mm), and kept separate in large stock tanks. Males were assigned to parental or sneaker category on the basis of their size (parental, TL 410 cm; sneaker, TL o9 cm) and length of the dorsal fin, according to Mazzoldi and Rasotto (2002). The water was kept at 181C and changed daily.…”

“…We tested the response of dominant males to the ejaculate of males performing different tactics in the black goby, Gobius niger L., a species in which pheromone production and the presence of alternative male mating tactics have been widely demonstrated (Colombo et al, '77;Colombo et al, '80;Mazzoldi and Rasotto, 2002;Rasotto and Mazzoldi, 2002).…”