I’m a granny! Sort of…

4 01 2010

I just got the news that the most recent healthy female cockroach I sent to Martyn at the Australian Museum in Sydney has laid at least one egg case! Here’s an excerpt from his email:

Good news – she WAS being sneaky. I noticed she had been getting surprisingly shy and was scurrying away and hiding whenever I went to check on her, while she had formerly been quite unconcerned. The local related species (Polyzosteria limbata – broad margined form) she is currently sharing a cage with is as docile as ever, so it was unlikely to be some recent disturbance.

On the weekend just past, she was a little slower off the mark than usual and I could see she was carrying an ootheca (egg case).

[The egg case was] smaller than I would have expected and of a relatively shiny hazelnut colour. I would think this is not her first so I will have to watch to try to see where she is hiding them but she is very alert to being watched – more so than I would have thought. The P. limbata simply dig a shallow hole and bury theirs and don’t seem to care if [they’re] being watched or not.

I don’t know if this makes you a granny for 2010? Just thought you’d like an update of good news!

I was surprised it took so long — I always thought cockroaches were prolific breeders and as she hadn’t laid an egg case some weeks ago, I suspected that she wasn’t pregnant when I sent her across in November. Looks like I was wrong!

Update later the same day: After asking Martyn about the gestation period and commenting that I thought it was a long time and maybe she’d been impregnated by her ‘roomie’, he wrote this:

She is in with about 20 of the P. limbata but most are still too young to breed and all have their own species present anyway – it’s usually only unmatched males that try to impregnate females of a different species and in invertebrates cross-breeding is either very rare or physically impossible due to the ‘key and lock’ systems of most invertebrate reproductive structures.

I’m pretty sure she was impregnated before she was caught but as to ‘gestation’ I suspect these are a bit of an unknown quantity as to both how long the eggs take to hatch (maybe not until next spring) or how long they take to develop within the female. The life histories of most of our native animals are poorly understood and even more so with insects and other invertebrates – we know far more about the pest species than any of the natives.

As mentioned though, she may have been hiding her earlier egg cases as the cage is about 50 cm square and has a number of pots filled with different soil types, a leaf-litter floor and some dead wood – all provided as potential egg laying sites. In most species kept you can see where activity has taken place but this one is certainly behaving in a different manner and so may be camouflaging either the site or (as occurs in some other species) ‘hiding’ the ootheca in plain view by glueing bits of detritus all over it. Unfortunately with their need for sunlight she is currently at [my] home on a deck until we are better set up here [museum] – so I only get to observe activity on the weekends and in the mornings and evenings. Mind you the others normally carry the ootheca for several days before stowing it away somewhere and are therefore easier to keep tabs on – this one doesn’t seem to do this – mind you it MAY just be this individual too!

I’ll keep you informed if I find any hatchlings. From the size of what I saw I’d guess about 10 hatchlings per ootheca.

Update October 2010: In late October, I got this email from Martin:

Just thought you’d like to know I saw your cockroach again yesterday and she was carrying yet another ootheca. I have now caught her out of the main cage and put her in a smaller one where I can better track the progress of the eggs. Anyway clearly P. cuprea is a very hardy long-lived species! They are also very good at escaping detection – I still haven’t noticed any babies but can’t discount them as the original female was so good at hiding that several times I assumed she was dead and started looking for her body, only to find her hale and hearty.

So I asked him what male she mated with, as he doesn’t have any other live specimens of this species. His reply:

Well that’s where it gets tricky. Most insects mate only once and store the sperm for the reproductive life of the female (this can be years). Some long-lived species mate several times over a long lifetime, and some, like certain beetles and certain cockroaches can mate with multiple partners and the eggs are either fertilised with a mix of sperm OR the next eggs laid get fertilised by the last male to mate with her – in the latter case, the earlier sperm are still viable but must now ‘wait their turn’. Needless to say this is what I am hoping is the case here as the other species in there with her – altho’ of the same genus – is of a different sub-set of that genus without the speckled legs. It is unlikely to be viable as a cross as a result OR maybe she’s laying blanks like a chicken does. The purpose of this segregation now is to see if the eggs hatch and what they look like.

Update November 2010: The babies from January have arrived! Here’s the latest update from Martyn:

Just thought you’d like to know that last year’s babies are starting to appear now in the cage. All look like perfectly normal P. cuprea, but all I have seen so far (about three, ranging from half grown to adult) seem to be females so it might be option 3 and the result of parthenogenesis, or it might be that this species throws more female offspring than males. Either way it is good news and the result is a success so far. If the colony can continue from here, that will be the next milestone.

Needless to say, I’m pleased. An unexpectedly overjoyed that she’s had healthy babies in the confines of an Australian Museum scientist who has a passion for these beasties!

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For other related articles on this cockroach saga, see these articles (in the order listed):


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31 08 2014

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