Leaders in agony

THE animal kingdom is inhabited bysome species which exist in groups orpacks, and these groups are led anddominated upon by individual male orfemale members. It had been believedfor long that animals which are subjugated are the most stressed and sufferfrom various problems like miscarriagesand failure to reproduce. New research,however, shows that it is the other wayround - the animal which dominates isthe actual sufferer.

Behaviourial biologists Scott andNancy Creel of Rockefeller University,New York, along with Steven LMonfort, an endocrinologist at theSmithsonian Institution's ConservationResearch Centre, Washington, us,report that dominant females in 14 packsof dwarf mongooses had the highestlevels of the stress-related hormone,cortisol. Similar studies on femalebaboons and male and female wild dogsindicate that dominance comes at a highprice. In baboons, it leads to higher ratesof miscarriages, while in dogs andmongooses persistent stress shortensthe lifespan of the alpha/dominantanimals (Science, Vol 271, No 5247).

The Creels' study is the first of itskind where hormonal levels have beenstudied in several free-rangingrather than captive species. The oldertheory about subordinates with higherchronic stress levels arises from studiesconducted on captive colonies ofrodents and primates in the '50s and'60s, They found that the subordinateshad higher cortisol levels and sufferedfrom ill health and reproductive failure.Higher stress levels in subordinatessupport the theory of dominance wheresurvival of the fittest was the mainfeature; the Creels embarked on theirstudy believing this. "We thought thatstress could be a factor in suppressingthe subordinates' reproduction," saysNancy Creel.

The researchers collected samples ofurine and faeces of mongooses and dogsto establish the basal stress hormonelevels for each species and to obsmeany disparity among individuals.Contrary to expectations, they foundhigher glucocorticoid (a corticoid thataffects glucose metabolism) levels inalpha males and females- probably as a resultof their aggressivebehaviour.

It is still unclear howthis phenomenon affects,the animals' health.According to behaviourial ecologist SamWasser of the Universityof Washington, alphafemale baboons do havehigher rates of miscarriages, but Wasser hasnot analysed stress hormone levels. Biologistshave not been able tofind a similar response inmongooses and dogs."They must be paying)port e the price in another way,perhaps a shorter lifespan," says Scott Creel.

The methodology adopted in thestudy has come under fire. According tocritics, the hormonal levels derivedfrom urine and faeces can never bethe same as that extracted directlyfrom the animals' blood. The accuracyin the time of collection and the levelof steroids in the animals' urine havealso been questioned. Notwithstanding its criticism, the study hasmade biologists realise the potentialvariety of relationships that can existbetween animal behaviour and hormones. "We are realising that hormonallevels are more and more situationdependent," says Jeanne Altmann, abehaviourial ecologist at the Universityof Chicago in US.