Pituitary and Nervous Control of Chromatic Responses,Especially of Xanthophores,in Killifish ( Fundulus )

Abstract

Previous work on killifishes has shown the yellow pigmentary effectors (xanthophores) of Fundulus heteroclitus and F. majalis to be subject to humoral control and to direct, probably double, nervous control permitting independence from melanophore responses. 1 A pituitary hormone dominates the xanthophores of the minnow Phoxinus, 2 as it does amphibian melanophores. Pituitary extract causes xanthophore pigment dispersal in this and other teleosts—including Fundulus. 3 , The present paper reports experiments undertaken to verify and evaluate the inferred participation of the hypophysis in pigmentary coordination, with respect chiefly to the xanthophores, in Fundulus.

Chromatic responses were determined in 54 F. majalis 5 or more days after total hy-pophysectomy, 5 i.e., when pituitary substances were absent from the circulation. Black-bottomed and white-bottomed vessels evoked darkening and paling, through melanophore change, about as readily as in normal fish (as in F. heteroclitus). 6 The hypophysectomized F. majalis were clearly incapable of normal adaptive response to yellow, however, irrespective of the duration of their stay over that color (instead of white or pale blue). Yet they became certainly, though only slightly, more yellowish after staying over yellow than otherwise. This fact was verified by reciprocal comparative tests, involving interchange of the yellow and other pale substrates. The xanthophores of the tail fin (as examined microscopically) after hypophysectomy did not effect the usual pigment-dispersing response to yellow, but they did respond to black, thus showing that pituitary intervention is not essential for eliciting their pigment dispersal.

In 20 F. heteroclitus the effect of total hypophysectomy on xanthophore response was greater. These fish remained uniformly grayish over a pale ground, whether yellow, white, or blue. Their caudal xanthophores showed none of the normal pigment-dispersing response to yellow (contra Matthews). 3 Nevertheless, these xanthophores could still show the temporary pigment dispersal that may be brought about by handling.