Crayfish_News_BaldryD, 19 March 2010
Male Form Alternation in Spiny-cheek Crayfish Orconectes limosus at Cessy (Central-eastern France):
The Discovery of Anomalous Form Males
Amicale des Pęcheurs de l’Etang de Cessy (APEC)
315 rue des Marguerons, 01170 Cessy, France
In 2009 a detailed study was made of the life cycle of the Cessy Pond population of Orconectes limosus (OCL). In all, 992 males were trapped and subjected to morphometric analysis, and study of their 1st gonopods (to distinguish Form I (FI) males, Form II (FII) males and juvenile males). The main features of 1st gonopods are shown in Figure 1.
Towards the end of June, when catches of FII males peaked and when FIs were absent from catches, it was noticed that a few FIIs had moulted into forms whose 1st gonopods had anatomical features that set them apart from both FI and FII males, and from the deformities that had previously been reported; see photos in Baldry (2009). When a greater number of those anomalous gonopods had been examined, it seemed likely that they were variously intermediate between those of FIIs and FIs.
That was surprising, considering that Faxon (1884) asserted that no intermediate forms occurred in the genus Cambarus. Furthermore, in more recent literature there does not appear to be any mention of intermediate male forms occurring amongst the many members of the Cambaridae.
Observations on OCL adult males and the morphology of their 1st gonopods. See Figure 1 and Photos 1 – 4
Figure1. Drawings of 1st gonopods as viewed from beneath the crayfish (based on many direct observations, photos and sketches). Abbreviations are: ex – exopodite (central projection); exs – exopodite stylets; exf – pronounced exopodite fold; en – endopodite (mesial process) bearing a patch of setae; ens – endopodite stylets (long, pointed and scythe-shaped in FIs); pr – protopodite bearing setae; te – terminal elements; GL – gonopod length; GW – gonopod width.
1 2 3 4
Photo 1. Anomalous gonopods. Salient features: overall whitish-cream colour, except for the pointed and splayed endopodite stylets which are tinted yellow and grayish; exopodite fold not very pronounced; and absence of protopodite setae.
Photo 2. Anomalous gonopods similar to those in Photo 1, but showing an unusual orientation of the terminal elements and pronounced exopodite folds.
Photo 3. Anomalous gonopods similar to those in the preceding photographs, but being partly darker in colour and having obviously pointed, tinted and splayed endopodite stylets. The exopodite folds and the protopodite setae are pronounced. A small spine can be seen on each protopodite (cf. Photo 6).
Photo 4. Anomalous gonopods similar to those in Photo 3, but more generally darkened and having well-defined and glossy exopodite folds. The protopodites lack setae.
The greatest numbers of anomalous form and FII males were examined from 25 June to 26 July. Actual numbers were 12 anomalous males (8.9%) and 123 FIIs (91.1%). Sizes of FIIs were: mean carapace length 36.4 mm (range 29.0 – 50.0 mm) and mean live weight 15.2 g (range 6.5 – 33.5 g). The Width / Length ratio of their gonopods was 0.20, the same as that given by Buřič et al. (2010).
Sizes of the anomalous males were: mean carapace length 41.1 mm (range 33.0 – 48.0 mm) and mean weight 18.0 g (range 8.5 – 19.0 g). Gonopod Width / Length ratios varied from ca 0.20 (similar to FIIs) to ca 0.22 (similar to the FIs).
All males had readily discernable spurs (hooks) on the ischium of the third pair of pereopods
Observations on the behaviour and fate of OCL anomalous form males
From late June, FI and anomalous form males were separately installed in identical semi-natural outdoor tanks together with adult females, and as far as possible, they were inspected daily, often as many as three times a day. The most noteworthy findings were that:
· Just like FII males, no anomalous form males engaged in courtship behaviour, nor did they mate.
· Some anomalous males moulted to the FI state (see Photo 5A & 5B) and mated with the females.
Photos 5. Photos of 1st gonopods.
5A shows the exuvium of the gonopods of an anomalous form male that moulted to FI on 21 August 2009. Although the exuvium has partly collapsed in on itself, obvious visible features include slight yellow tinting of the terminal elements, pointed and splayed endopodite stylets, and the remnants of exopodite folds. The pre-moult gonopods were of the type shown in Photo 3.
5B shows the gonopods of the FI male that emerged from the exuvium shown in 5A. They reflect the features presented in Fig. 1, i.e., the soft and flexible exopodite stylets that are partly tinted yellow-amber; the longer, rigid, sharply-pointed and scythe-shaped endopodite stylets whose tips are only faintly tinted; and pronounced exopodite folds.
In November 2009, two anomalous males were put into an indoor aquarium, to prevent them from freezing to death outside. They were inspected daily. When examined on 15 March 2010 they were both alive and their gonopods were in an anomalous state. One of them, which was found dead on 20 March 2010 is discussed below.
In contrast to the comments made on FII and anomalous forms above, FI males mated continuously from late July until the end of November, when they were destroyed.
The 1st gonopods of the anomalous male found dead on 20 March 2010. See Photo 6
On first examination, the most obvious, unusual features of the gonopods were: i) darkening of the gonopods distal to the protopodites, especially of the endopodites, ii) exopodites that projected well beyond the endopodite stylets (the reverse of what is seen in FII and FI gonopods), and, iii) the overall untidiness of the surface texture.
A closer examination revealed that there was a small robust spine on each of the protopodites (see Photo 6). Such spines had not been noticed on the published illustrations that the author had consulted. However, the spines that are visible in Photo 6 are not unique to that specimen; they also appear on the gonopods shown in Photo 3.
Photo 6. The gonopods of the male that was found dead on 20 March 2010. Comments are given in the text.
Literature searches for information which might have assist in interpreting the Cessy observations were not very productive, but an interesting remark was found in Hobbs et al. (2007); to quote: “For reasons not understood, however, sometimes a molt of the quasi-juvenile does not result in a transformation of the animal to the adult, first form” state.” Regrettably, that remark is insufficiently precise for us to determine if it was meant that an FII molted and transformed to another FII (which is known to occur), or whether it transformed to something which may have been akin to the anomalous males that this author has reported.
It is thus hoped that by writing this article, the author may be able to identify colleagues who have noticed anomalous form males in the genus Orconectes (or related cambarid genera). Meanwhile, it is pertinent to make a few comments on male form alternation, as observed at Cessy.
Putting aside the male that was found dead on 20 March (and appears to be in a class of its own), the morphology of the 1st gonopods of all the other anomalous males seem to suggest that they represent individual steps in a gradual transformation process from FII to FI that has been prematurely terminated before the definitive FI stage was attained.
That possibility could be due to an imperfection in the mechanism that synchronizes the anatomical transformation of the gonopods, and, the ecdysis process. In other words, the ecdysis process may have been concluded before the complex morphological transformation of the gonopods was complete. That sort of situation could result from a temporal shift of the ecdysis process and/or of the transformation process; presumably due to a change in the balance between the hormones responsible for the two processes.
It is appropriate to conclude by quoting from the memorial lecture of J. F. Payne (Payne, 1997): “Thus considerable variation on the cyclic dimorphism theme occurs, but few studies of cambarid life cycles have investigated potential variations from the traditional From I – Form II cycle. Additional work is necessary to determine the prevalence of different modes of adult male development.”
Finally, the author wishes to thank David Holdich, Chris Chucholl and Williame Coosemans, all of whom provided assistance during the planning and/or implementation of the 2009 Cessy studies.
Baldry, D. (2009). Abnormalities seen in Orconectes limosus from France. Crayfish NEWS, 31(3) :8-9.
Buřič. M, Kouba, A. and Kozák, P. (2010). Molting andGrowth in Relation to Form Alternations in the Male Spiny-Cheek Crayfish Orconectes limosus. Zoological Studies, 49(1): 28-38.
Faxon, W. (1884). On the so-called Dimorphism in the Genus Cambarus. Amer. Jour. Sci., 27: 42-44.
Harris, J.A. (1901). The dimorphism of Cambarus, I. Kansas University Quarterly,10(2): 49-59.
Hobbs Jr., Harvey, M.C. and Hobbs III, H.H. (2007). A Comparative Study of Functional Morphology of the Male Reproductive Systems In the Astacidae (Crustacea: Decapoda) with Emphasis on the Freshwater Crayfishes. Smithsonian Contributions to Zoology, Number 624; 76 p.
Payne, J.F. (1997). Adaptive Success within the Cambarid Life Cycle. Freshwater Cratfish, 11:1-12.