Post-embryonic development of the lateral eye of Cloeon sp. (Ephemeroptera: Baetidae) as revealed by scanning electron microscopy

Post-embryonic developmental patterns of the lateral eyes of both male and female Cloeon sp. are described and compared with each other morphometrically on the basis of scanning electron microscopy. In the larvae number of ommatidia, ommatidial size, and total corneal surface area of the eye increase towards the subimaginal moult. It is then that clear differences between males and females begin to occur: while further increases in the number of ommatidia are recorded from the lateral eye of subimago and imago females (accompanied by decreasing facet sizes and interommatidial angles), males show decreasing numbers of ommatidia and total corneal areas in their lateral eyes as they prepare to leave the water. Consequently, the lateral eyes of a female are larger than those of a male imago. It appears that the enormous development of the dorsal eyes of the males has occurred at the expense of the lateral eyes. In male as well as female lateral eyes two major facet shapes are encountered: squares with rounded corners which are predominantly found in the central and upward looking areas, and hexagons which are dominating the lateral and ventral-facing regions. The different roles of the lateral eyes in male and female baetid mayflies is discussed in relation to their flights and the intriguing idea is presented that females might choose males with the largest dorsal eyes