THE BREEDING CHARACTERS OF PALAEMONETES VARIANS (LEACH) (, )

BY

L. J. ANTHEUNISSE, N. P. VAN DEN HOVEN Department of Zoology, Free University, Amsterdam, The Netherlands

and

D. J. JEFFERIES Department of Zoology, University of Liverpool, England 1)

During an ecological study of moulting and growth in Palaemonete.r varian-f (Leach, 1814) carried out at the University of Liverpool (cf. Jefferies, 1964) and as a start of endocrinological studies of internal breeding factors in the same species done at the Free University, Amsterdam, the relative lengths of the berried ( egg-carrying ) intermoult and normal intermoult periods were examined together with the details of the breeding dress. This information was obtained by following the individual moulting histories of female specimens of Palaemonetes variants (collected from sites near Liverpool and from the Dutch North Sea island of Schiermonnikoog) maintained in separate brackish water aquaria in the laboratory at room temperature (Free University, Amsterdam) and under natural thermal conditions (University of Liverpool). The were easy to keep with a diet of tubificid worms, green algae (Ulva) and dry fish feed. A daily inspection of the aquaria for the presence of exuvia provided us with the durations of the inter- moult periods. An accurate examination of the cast exoskeletons following normal and berried intermoult periods showed the details of the modifications occurring in the integument at breeding. These breeding characters are noted below and compared with those of another palaemonid prawn in which they are known in detail, elegant Rathke (cf. Höglund, 1943 as Leander .rquilla (L.)). The possible internal and external factors involved in the breeding moult are then discussed. -

THE BREEDING DRESS

During the breeding period, the integument of the female Palaemonete.r varians undergoes important modifications characterized by the presence of extra setae for the purposes of egg bearing. This special breeding dress comes into being at

1) Now at Monks Wood Experimental Station, Abbots Ripton, Huntingdon, England. 260

the moult preceding copulation and ovulation and is lost at the moult after hatching. Such a breeding dress is found not only in Palaemonetes but also in other Palaemonidae and throughout the (Yonge, 195 5 ) . Curiously these important changes during the breeding period of the Natantia remained unobser- ved for a long period; the first reports being very incomplete. Ehrenbaum ( 1890 ) , working on Crangon, mentioned the appearance of certain setae exclusively during the berried intermoult period and Mortensen (1897) reported a single breeding character of Palaemon adsperJus Rathke (the long plumose setae on the endopo- dites of the first pleopods). Nothing more was published on this phenomenon until the practically simultaneous papers of Gurney (1923) and Sollaud (1923). These authors, working on species of Palaemon 2) and Palaemonetes, noted that certain setae appear in these animals only when the females moult into the egg- carrying condition. Sollaud in this connection distinguished between permanent and periodic secon- dary sexual characters; the former persisting after sexual maturity, the latter appearing only during the berried intermoult period. Among the permanent secon- dary sexual characters in the female he included: ( 1 ) the enlargement of the epimera of the three anterior abdominal segments; ( 2 ) the enlargement of the sternal parts of the same segments; (3) the length- ening of the three anterior pairs of pleopods by the addition of a praecoxa; (4) the development of a flange on the basipodite of the three anterior pleopods. Only the special setae of the breeding intermoult he termed periodical. Neither Gurney nor Sollaud gave complete and accurate accounts of the breeding setae, and it was left to Hoglund (1943) to give a fully comprehensive report on the breeding dress of the palaemonid prawn Palaemon elegan.r (for which he used the name Leander .rquilla (L. ) ) . As noted by Jefferies (1964) the breeding dress of Palaemonetes varian.r is very similar to that described by Hoglund for Palaeyrzon elegans} but there are some slight differences, mentioned in this paper with a description of the breeding characters. a. The enlargement of the brood-pouch

With regard to Sollaud's first two permanent secondary sexual characters, H6g- lund was not in agreement. In contrast to Sollaud's opinion he regarded them as periodical breeding characters, resulting in the enlargement of the incubation chamber during the berried intermoult period. Investigations of these characters in Palaemonetes varian.r (tables I and II, University of Liverpool) show that, as in Palaemon elegan.r, a wider abdomen in the female appears to be in a way a permanent secondary sexual character, being much wider than in males of a corresponding size. However, as demon- strated by H6glund for Palaemon elega1qJ, Palaemonete.r variants also shows a

2) These authors, like many others, employed, incorrectly,the generic name Leander for Palaemon.