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Feminist 



Bacteria of 



Ladybird 



Beetles 



A dose of antibiotics can clear up 



many problems, including a 



biological puzzle 



by Gregory Hurst and 

 Michael Majerus 



Like humans and many other animals, 

 the two-spotted ladybird beetle tends to 

 produce sons and daughters in approxi- 

 mately equal numbers, sex being deter- 

 mined by the genetic constitution of the 

 father's sperm. Fifty years ago, however, 

 Ya Ya Lus — a Russian scientist breeding 

 ladybirds in the attic of his house — no- 

 ticed that some females produced mainly 

 daughters. Intriguingly, these females also 

 laid many eggs that simply failed to hatch. 

 Lus performed an analysis of this odd phe- 

 nomenon and showed that the mother, not 

 the father, was apparently responsible for 

 the plethora of daughters and that the 

 dearth of sons was due to the death of male 

 embryos early in their development. Un- 

 fortunately, with the information available 

 to him, Lus was unable to determine how 

 this strange state of affairs came about. 



The story of male ladybird mortality 

 was recently taken up in the United King- 

 dom, where field research into the mating 

 preferences of these beetles had turned up 

 similar skewed sex ratios and where 

 breeding experiments in the lab had deter- 

 mined that, as in Lus's attic, females were 

 behind the superabundance of daughters. 

 And, as Lus had also noted, only certain 

 ladybird "families" were involved. To find 

 out more, we began our real detective 

 work. 



Genetic material in the nucleus of a cell 

 comes from the mother and father in equal 

 proportions, but there is far more to an or- 

 ganism than its nuclear genes. In fact, the 

 vast proportion of any new individual is 

 made up of cytoplasm, all the protoplasm 

 in a cell outside the nucleus. This cyto- 

 plasm also contains genetic material. In 

 most kinds of organisms, a new embryo is 



formed following the fertilization of an 

 egg cell (which contains large amounts of 

 cytoplasm) by a spermatozoon (which 

 contains very little). The genes in the new 

 organism's cytoplasm thus come almost 

 exclusively from its mother. 



Cytoplasm genes are less numerous 

 than nuclear genes, but they may be of 

 many types. Some, such as mitochondria, 

 may be essential to such basic cell func- 

 tions as energy production. Other genes 

 may come in the form of viruses, proto- 

 zoans, or bacteria that Uve and reproduce 



in the cytoplasm of their host cells and are 

 passed along with the rest of the genetic 

 material in the reproductive cells of their 

 host. 



As we set out to track down the killer of 

 our male ladybird embryos, we followed 

 the scientific dictate, "Do easy, cheap ex- 

 periments before difficult, expensive 

 ones." And since previous work by others 

 had turned up male-killing bacteria in 

 other situations, we adopted an approach 

 familiar to physicians; "If there is a suspi- 

 cion that the problem is caused by bacte- 



32 Natural History 6/94 



