Courtship and reproductive behaviour in newts and salamanders
Courtship behaviour in newts and salamanders is very different to that of frogs and toads (anurans). In anurans, fertilisation is external so the male expels his sperm whilst the female lays her eggs. However, in newts and salamanders, fertilisation is internal. The male deposits a sperm package, the spermatophore, and the female uptakes this into her reproductive tract to fertilize her eggs. Male newts and salamanders have evolved a range of complex behaviours to encourage the female to uptake the spermatophore. This may involve contact between the male and female, but in aquatic newts of the family Salamandridae, there is no contact and the male encourages the female through complex courtship displays.
Newts in the genera Triturus (e.g. great crested newt) and Lissotriton (e.g. smooth newt), have similar courtship displays. During an initial orientation phase, the male will move in front of a female and attempt to gain her attention. The female may show no interest and swim away. If successful, the male moves into a static display which involves intense tail fanning and wafting pheromones towards the female. Once the female is fully engaged the male will start to retreat backwards facing the female, still tail fanning. He will then turn around, creeping away from the female with his tail quivering and her following. The male will pause, deposit his spermatophore onto the substrate, walk one body length forward and stop, turning 90 degrees. This allows the female to move so that her cloaca is directly over the spermatophore. She now uptakes the spermatophore for successful fertilisation. Unfortunately, spermatophore uptake by the female will not always be successful so the male has to perform the courtship display from the beginning.
Although males will develop secondary sexual characters during the spring (e.g. tail crest, webbing on the feet), the courtship display takes place in underwater in darkness, so visual cues are likely to be irrelevant. Recent research has shown that the courtship pheromones produced by the male are crucial in ensuring mating success. When a male employs tail fanning, he sends sex-specific pheromones towards the female and these directly impact her responses. In the laboratory, female palmate newts (Lissotriton helveticus) exhibit all the sexual responses up until spermatophore uptake, when in the presence of male pheromones, but no male present. This demonstrates the importance of pheromone production and effective transfer to the female during mating. Previous research has demonstrated that male newts which perform their displays more energetically, have higher mating success. In addition, in male smooth newts (L. vulgaris), males with higher body mass and crest height achieve higher mating success, possibly due to enhanced pheromone production and more effective transfer to the female. This research demonstrates the importance of effective transfer of pheromones by the male towards the female for reproduction.
Male pheromones may have additional effects on females. In the aquatic Spanish ribbed newt (Pleurodeles waltlm), which has both contact and non-contact displays, the male has special glands in the cloaca. When these are released they induce the female’s cloaca to expand and uptake the spermatophore. It has previously been thought that the female doesn’t have a choice over whether she receives the spermatophore from a particular male, once he has clasped her and released his pheromones. However, recent research has demonstrated that females of this species may exhibit thanatosis (feigning death) during courtship prior to the crucial moment of pheromone production by the male. This avoids spermatophore uptake by the female and therefore may provide an escape strategy by a female, should she not want to be persuaded by the male to mate. Thanatosis has previously only been known as an escape strategy by amphibians and has not been observed in a sexual context.
Male newts and salamanders exhibit a range of complex sexual displays. Although many of the behaviours exhibited are widely understood, there are still areas where we have less understanding, such as the effects of pheromones, importance of secondary sexual characters and female choice in mate selection.
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