I would like to perform a study that looks at the reproductive success rates of different sex ratios of crayfish (at natural densities). I wanted the response variables to include proportion of mature females successfully mated (as indicated by extrusion of eggs) and clutch size (controlling for female size). However if eggs are extruded regardless of successful copulation occurring then such responses would give a false impression of reality. Also perhaps the number of eggs extruded is not representative and in fact I should be assessing number of eggs successfully fertilised. Is there a way to achieve this by identifying developmental stages of the egg? Ideally I don't want to have to wait over the entire period of berry to get the answers (i.e. count hatchlings).
Dear Rupert,
In lab culture I notice that non-mated females sometimes put on eggs. Usually these turn pale after a few days and are then discarded by the female. Fertilized eggs should turn dark and increase in size over time. I my experience hatching success is not similar to clutch size but I have no additional information on fertilization success to cross-ref this observation. Of course making microscope slices from eggs is a possibility and will provide an answer to your fertilization question. But why not do the whole period indeed and see the number of offspring (and their survival in different densities) ... in the end that is what matters for the development of the population is it not?
Best regards,
Ivo Roessink
Hi Rupert
An interesting series of questions! Like Ivo, I have occasionally noted some female A. pallipes to extrude eggs although not mated, perhaps in response to male pheromone in the water, As for fertilisation, in 1991 Celada, Carral and Gonzalez published photos of fertilised eggs at various stages of development, visible without sectioning. There are many works comparing ovarian and pleopodal egg counts which should give you an expected ratio. You can also speed up development by temperature manipulation.
Best wishes
Julian Reynolds
Hi Robert.
Maybe this article will be benefit for you. "Successful sex ratio of 1M:4F in the astacid crayfish Pacifastacus leniusculus Dana under captive breeding conditions".
Also there are many references that cited in this study. Maybe they are use full for you.
Hi Rupert,
in the case of signal crayfish, we also found out some females which can extrude their eggs without previous mating, but the eggs are lost in following weeks. Other females do not spawn and resorbe their eggs. Unfertilized eggs do not pass different developmental stages and you can therefore check them.
Successful mating you can observe by deposited spermatophores on the ventral side of the female body. However, be careful because females, when disturbed at the beginning of egg laying, often stops spawning which leads to internal eggs resorption of eggs.
Best regards
Milos
Hi Rupert,
It shouldn't take long for you to notice embryonic development of the blastula by sampling a few eggs and checking under the microscope. Just note that the outside embryos from the mass will be slightly more advanced in development as less oxygen limited so these will be better representative of fertilisation success.
Stephen
Hello everyone,
Thank you for the excellent detailed answers. It seems to me that spawning without successful copulation is indeed something that I need to be aware of but is rare. It also seems that there will be ways to quantify the proportion of fertilised eggs anyway by microscope inspection which is what I ultimately want to know.
Ivo, you are correct in your suggestion of leaving the females to over-winter. Ideally I also want to incorporate egg mortality into my study. This question really comes down to practical constraints- if I can do this I will.
Milos (and others!), in the population I have studied, berried females appear in catches at the end of September/ early October). What would you say is a safe period of time to wait before collecting the females so that females will have finished spawning and I will not disturb egg laying and encourage resorbtion?
Thanks for all your answer, they have been very helpful.
Cheers,
Rupert
Hi Rupert,
Interesting study I like the sound of it. It is Hard to answer your question as each females ability to tolerate the handling stress will vary. I always found with crabs that they were fine being sampled for embryos on separate days fairly consecutively but multiple sampling and prolonged sampling stressed them the most. So be wary of that when you get in your groove. Also the longer she carries and the more developed the embryos the less likely to abort. However you have to check them sometime so do it quickly and they should be fine. I think you should look up the typical brooding time for the species and take in to account water temperature. You will know by the brooding behavior of the female if the eggs are developing as she will be ventilating them and so you can start to gauge other females based on the same
thing. I wouldn't worry too much about resorption just be swift and gentle when you sample and all should be fine.
Hope this answers in part some of your questions.
Good luck,
S
- Badges
- Science topic
- Similar topics
- Publishing