Reproduction, Body Condition and Dietary Variation of the Lesser Siren (Siren Intermedia)

Date of Graduation

Summer 1999


Master of Science in Biology



Committee Chair

Alicia Mathis


I collected life history data for a population of an aquatic salamander, the lesser siren (Siren intermedia), in southeastern Missouri. I used gonosomatic indices as an estimate of gonad activity to delineate the reproductive cycle. Testicular activity peaked in February followed by a decline in March, and ovarian activity peaked in January and February followed by a steep decline in March. Gamete maturation was synchronous and reproduciton appeared to be annual. Clutch sizes ranged from 280 to 701 with a mean of 419. All mature females collected in February were gravid, and three contained oviducal eggs. All mature females collected in March had oviposited. Clutch size was positively correlated with female body size (SVL). I estimated the body condition of adult male sirens using a mass/length regression analysis and found that breeding males were in poorer body condition than nonbreeding males. Dietary analysis showed that sirens are generalists consuming a wide variety of prey taxa, although cladocerans were the predominant prey taxon in terms of frequency and total number. Sirens had the second lowest dietary niche breadth that has been estimated for any aquatic salamander, due in part to the disproportionate number of cladocerans. Males captured during the reproductive period had significantly lower volumes of prey than nonbreeding males. The difference in body condition and prey volumes between the two seasons suggests that there is competition between breeding males for females and/or other resources. In addition, parasitic infection had a negative effect on body condition. Seventeen individuals were infected with the cestode Proteocephalus sireni. Parasitized individuals were in significantly poorer body condition than nonparasitized individuals.

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© Aaron Michael Sullivan