A) Micrograph of the anal fin (4X); B) Circular smooth muscle (20X); C) Longitudinal smooth muscle and dense fibrous connective tissue (20X); D) Intromittent
organ (20X); E) Fin rays and dense fibrous connective tissue (20X).
In reptiles, an intromittent
or copulatory organ is observed in all living species, with the exception of Sphenodon sp.
Kennedy defined his species groups solely on morphology of the intromittent
penes, so it is satisfying that we find similar patterns based on molecular and morphological characters not used by Kennedy.
These include differences in external reproductive anatomy--males possess elongate intromittent
organs (claspers) whereas females do not; differences in size--females are often larger than males (7, 8); differences in tooth morphology--many male batoids possess cuspidate teeth to grip their female mates during courtship and copulation (9-11); and differences in skin thickness--some female sharks and rays possess a significantly thicker dermis than males (12, 13).
Scientists don't know when the fish reach their sexual maturity, how often they reproduce, or even how they mate--the male fish has no obvious intromittent
For example, a male's fertilization success (number of eggs fertilized per copulation) can be affected by both competition with other males (e.g., specialized intromittent
organs that remove the sperm of rivals; Waage 1979) and mate choice (e.g., ejection of sperm by females; Birkhead and Hunter 1990).
The researchers used a laser ablation technique to cut off tiny "intromittent
" spines on the genitalia of virgin male D.