Abstract
In the Bahamas, interspecific groups of Atlantic spotted dolphins, Stenella frontalis, and bottlenose dolphins, Tursiops truncatus, have been observed underwater since 1985 on Little Bahama Bank. Mixed-species groups engage in associative behaviors and aggression on a regular basis. Because of their complex cognitive behaviors and large brain encephalization, dolphins are likely capable of complex social interactions, even between species.Between 1993-2003, 177 Mixed-Species Encounters (MSE) were categorized by the age class of male spotted dolphins, the ratio of spotted dolphins to bottlenose dolphins, behavior as Associative (traveling, babysitting, play) or Aggressive (chases, mounting, head to heads) and by directionality of sexual behavior. The majority (68%) of MSE involved adult spotted dolphin. Associative behaviors were observed more than aggressive behaviors in groups where no adult male spotted dolphin, only male calves, or male juvenile spotted dolphins were present. Aggressive behaviors were observed more frequently than associative behaviors in adult male spotted dolphin groups. When groups were unbalanced in favor of one species or the other, differences in social interactions occurred. Male spotted dolphins were never observed attempting to mount male bottlenose dolphin although they chased them. Despite the larger ratio of male spotted dolphins to bottlenose dolphins during MSE, directionality of male-to-male sexual contact was primarily one-way. Male bottlenose dolphin mounted and copulated with male spotted dolphins but not the reverse. Opportunities for cross-species mating and hybridization clearly occurred. Male bottlenose dolphins copulated with female spotted dolphins and male spotted dolphins copulated with female bottlenose dolphins. These sympatric dolphins in the Bahamas have a complex and dynamic relationship that varies with sex and age and revolves around potential reproductive isolation issues.
Highlights
Title Directionality of Sexual Activities During Mixed-Species Encounters between Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus)
In addition to interspecific group interactions, individuals have been documented in complex situations including an individual common dolphin (Delphinus delphis) with bottlenose dolphins (Tursiops truncatus) by Bearzi (2005), an individual long-finned pilot whale (Globicephala melas) with Atlantic white-sided dolphins (Lagenorhynchus acutus) by Baraff and Asmutis-Silvia (1998), and an individual Risso’s dolphin (Grampus griseus) with striped dolphins (Stenella coeruleoalba) and common dolphins (Frantzis & Herzing, 2002)
When tested for a species advantage during Mixed-Species Encounters (MSE), the ratio of spotted dolphins to bottlenose dolphins was greater than 1:1 significantly more often when adult male spotted dolphins were present than when all other age class categories were combined (Pearson’s X2(1, n = 177) p < 0.001)
Summary
Title Directionality of Sexual Activities During Mixed-Species Encounters between Atlantic Spotted Dolphins (Stenella frontalis) and Bottlenose Dolphins (Tursiops truncatus). Long-term interactions between sympatric Atlantic spotted dolphins and Atlantic bottlenose dolphins in the Bahamas have been observed consistently every year since 1985 These two species have been observed in mixed group interactions and spend 15% of their time engaged in interspecies activities including foraging, traveling, play, alloparental care, aggressive activity and interspecific alliances (Herzing & Johnson, 1997). In addition to interspecific group interactions, individuals have been documented in complex situations including an individual common dolphin (Delphinus delphis) with bottlenose dolphins (Tursiops truncatus) by Bearzi (2005), an individual long-finned pilot whale (Globicephala melas) with Atlantic white-sided dolphins (Lagenorhynchus acutus) by Baraff and Asmutis-Silvia (1998), and an individual Risso’s dolphin (Grampus griseus) with striped dolphins (Stenella coeruleoalba) and common dolphins (Frantzis & Herzing, 2002)
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