Thursday, 31 October 2013

A Gynandromorph: This is a case where Arthur is Martha!

This appears to be a rather typical-looking Raspy Cricket. Raspy Crickets are members of the family Gryllacrididae. They are crickets but very different from the average field cricket one is familiar with. These crickets have the ability to spin silk with their mouthparts. They do this to construct enclosures where they spend the day. They tie leaves together or construct underground burrows that are stabilised with webbing. They even  provide the burrows with a cap that keeps them sealed in a waterproof and predator-proof enclosure when danger threatens. Perhaps, the most important feature of an underground burrow in the desert is to reduce the problem of water loss through evaporation.

What is interesting about this cricket is that it is a gynandromorph, that is, it is a creature that possesses both male and female characteristics. As an entomologist involved with fieldwork for over 60 years, I guess that I have come across fewer than a half dozen insects illustrating this phenomenon. The most spectacular are those that are bilateral, that is, where half the insect is male and the other half is female. Butterflies illustrate this best and can be very spectacular. But not all gynandromorphs are bilateral. The most usual cause for this malady is an "event" early in life at mitosis when cells are dividing and the chromosomes are recombining. Gynandromorphism probably leaves the individual sterile and unable to reproduce.

This cricket is not a true bilateral gynandromorph. It probably fits into the "oblique category as will be seen below.

Viewing the top of the head and pronotum, one can see nothing amiss. Everything appears normal. Similarly, a frontal view conveys a normal gryllacrdid appearance.

Gryllacridids are not known for outward sexual dimorphism except genitalically. In this respect they are truly spectacular, especially in males. The male genitalia displays an intricate array of hooks, claspers and modifications that provide examples of the old "lock and key theory", that is, the male genitalia are of a morphology that they will only work in females that of the same species. This theory has been challenged over the years but it is useful to make a point. In all the gryllacridids that I have examined, the male and female genitalia are highly distinctive. As a result they are the most useful taxonomic characters.

In more typical crickets (family Gryllidae) where males produce song, the wings are structurally modified for sound production. Gryllacridids also produce sound but in a different way. Individuals of both sexes in all stages of development can produce rasping sounds--hence the common name. Both sexes also "rasp" during courtship. 

They produce rasping sounds by inflating the abdomen slightly and rubbing pegs on the abdominal segments against a raised series of minute bead-like projections found on the inside of the adjacent hind femur. Other related families produce sounds in that same way.
 In this specimen the line of pegs are on the first and second abdominal segments. These pegs are actually modified hairs. They are at least generically characteristic and many were reviewed in several Australian genera by Rentz and John (1990). 
The pegs up close.
The inside of the hind femur.
A close-up of the bead-like structures that are rubbed against the pegs on the adjacent abdomen. 
Back to the odd features displayed by this cricket.

This individual has a part of an ovipositor. The normal ovipositor has two main parts that are divided down the middle. In this specimen we see the right side of what appears to be the right half of the ovipositor. Gryllacridid ovipositors are normally straight and long, about half the length of the insect itself or even longer in some species. Since this cricket had to undergo several moults in becoming and adult, it appears that the ovipositor did not develop properly and part was lost or broken after moulting.
This shows that there is just a half an ovipositor. The left half is missing. 

The V-shaped plate at the base of the ovipositor is the subgenital plate. this strucutre is normally sexually dimorphic and if this were a true bilateral gynandromorph, each side would have a very different structure. But here it appears symmetrical.  Note the little brown sclerite at the base of the filamentous cercus on the right.

These photos show the abdomen from above. The ovipositor is deformed, the right half which is twisted and pointed to the left. The white fleshy bits are usually possessed by males, females have a more sclerotised tip of the abdomen. This is unusual in this example. The small sclerite on the right at the base of the cercus may be a significant part of the normal male genitalia and the black ridge on the left is a feature found in males of some species. 

This is a most unusual gynandromorph. The internal morphology would show testes on one side and ovaries on the other if this were a bilateral gynandromorph. These features have not yet been examined on this specimen.

But what genus and species is this cricket? Based on the arrangement of the pegs on the abdomen, I would place it in Mooracra. Should we find additional specimens at this locality, we can provide a more authoritative identification.

There is a remote chance that his cricket is not a gynandromorph at all. It's deformity may be from some other cause such as parasitism. If so, this is the first time I have found such an anomaly.

Reference
Rentz, DCF, John, B. 1997. Studies in Australian Gryllacrididae: Taxonomy, biology, ecology. and cytology. Invertebrate Taxonomy, 3: 1053-1210. 

2 comments:

Assis de Mello said...

Hello Mr. Smiley!
What a nice creature!
My former student, Marcio (you met him in China), and I are just about to describe a case of bilateral gynandromorphism in a phalangopsid cricket from Brazil. Perhaps you can help us find some bibliography regarding that phenomenon in Orthoptera...

Assis de Mello said...
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