Differences in the Morphology and Reproduction of the Ascidian Boltenia Villosa Across a Latitudinal Gradient

While the larval and early juvenile stages of the stalked ascidian Boltenia villosa are well-documented in the literature, little is known about the range of morphological variation in B. villosa adults. Anecdotal evidence suggests that larger individuals with shorter stalks make up the populations found in Washington, while Oregon populations consist of smaller individuals with longer stalks. The present study aimed to develop a qualitative understanding of the morphological and reproductive differences across the latitudinal gradient of B. villosa. Morphological differences between populations were studied through a combination of morphometrics and scanning electron microscopy. To compare reproductive outputs, the diameters of oocytes and the gonadosomatic indices of representative individuals were measured. The results suggest significant differences between the two populations in body proportions, spine character, and reproduction despite their genetic similarities. These preliminary results provide the basis for future research into the distribution of B.villosa and the possible existence of an undescribed subspecies of B. villosa.