The genetic and molecular basis of developmental stability: the Lucilia story

would be giventhe 0th~. No amcsuntof training could stop her drum choosing six (receiving one). But with the nmmerats alone-that is. when the task was dissociated from the visible reward - she very quickly mastered the trick of getting what she wanted”. Even more fascinating is Wanscr’s discovery that adult rhesus mankeys have the ability to compute different objects (1 apple + 1 orange = 2 things), a skill that infants gain only when they have mastered object naming at around one year old. Hence, ii seems that Eanguage is not actually necessary for property- or kindindivtduation, as was previousljr assumed. Despite the fact that humans are not closely genetically related to birds, they o exhibit striking similarities in behav9ur, for example, monogamy, mate yuarding and song learning. Birds also provide patent evidence of evolutionary pressure shaping a species’ brain. Daviil Sherry (University of Western Ontario. Canada) has found increased ~~~~~~9ca~~~~~~~~ size in birds that hide food (Covidae. Paridae) 09 parasitize nests (M9lolhru.s oter). Shc~ry cautions that ‘it is scientifically incorrect to infer b~rna~ adaptations fro non-human species.’ But, Roger S!-separd’s (Stanford University, CA, USA) dr.~ovsry of men’s superior mental rotational ability

---..

hints at a clutch of anahpx adapEia/e motors that may have shaped th2 human mind according to gender-determined roles. Alex Kacelnik (Oxford University, UK) has drawn. an intriguing lir~kbetween birri ;md human resource management. ‘Discounting‘ is the way that an individual assesses the value of a resou9 ce today versus its value in the short-, medium- and long-term future. Starlings’ “risk aversion’, that is, the tendency to play it safe, izacreases as their ‘budget’ increases and vice Versa - with lttkfe to to:%?they are more prepared to gamble. By testing undergraduate students usiq a specially &signed compnter game, Kaceh9lk founad the human dtscounting c .Irve to be c~actly the same. But is knowing why we are the way we arc practicatly us&C Leda Cosmidrs thinks so: ‘by lmderstandin~g what k&nd of mental ~~~~9~~~~~~~~es we have. it might be possible to figure out what method of teachimg mathenniit irs wit0 99~the most eftcctive or PLOW to eliminate nygressic9n and war.’ Knowing that the hunter-gatherea mind is adapted to life in group!i of at most IO0 is a clue to some of the problems of nation state organization. ReaPimingthat we are programmed to fee? secure when

.-..--

he gemeticand molcc~al;~r mectw nisms responsible for ensuring phenotypic constancy In the face of develop mental and environmental perturbation (so-called devef~~mentai stability) have long been topics of interest among evolutionary and developmental biologists. Many well-known researchers, including Dobzhansky, Lewontin. Beardmore, Mather Parsons, Reeve, Soul&, Thoday dington have all touched on the and topi some time during their careers over 500 research n the area during the ve progressed very little in the understanding of these me&anisms. A group working out of t&e Departradeul of Genetics at the University of ha, under the leadern5e has, over the past 10 years, accumntated a growing body of data thet may alirr this. Using the evojution of insecticide resistance in the Australian sheep blowfly, Lucifie cqMicl, as a model, McKenzie and colleagues have identified a series of major genes influencing

slahility. This modcf uffcrs tlie n,otcntial for defining the genetic and ~~~(9~ec~~la~ bases of developmental stabiltty in one evolutionary system. Before the introduction uf a pesticide, The most commonly used estimator of resistant genotypes will be at a selective developmental stability has disadvantage as evidenced by tbe general ating asyK~~metry. that is, r rarity of resistance alleles in populations. ~~~ect~o~ai differences in character exUpon the introduction of a pesticide. these pression between left and right skies of a genotypes bc~omi~ selcctivcfy favoured normally bilaterally symmetrical o and rapidty spread ~~~~~~~g~~~)ut the popuisml. It is assumed that the develop lation”. The ~~~co~f~~9~at~o~ of tfiesG>novel of each side of a bilateral character is conalleles into a genome is believed to result trolled by an identical set of genes, and in disruption of coadapted gene complexes therefore any observed differences in exthat may have pleiotropic phrnotypic pressiorm between the two sides must be consequences. After resistance hecomes environmental in origin and relfeck differences

encoelnte,‘fd

by the

t’(A,o sides

dur-

ing development. The degree of difference therefore reflects the degree of developmental stability of the character as a whole; the greater the differences the poorer the stability. This hypothesis has c~~~~~~~~~e~ ho the use of %Iuctuating asy~~~~e~I-yas an indicator of developmental stress on organisms”. Until recently, two major genetic phenomena have been postulated to

wirlesgmact, p’“ticitle cations

continued may

favcpur

setrctioi~

by

#enol?lic

Hdifi-

the

that ameliorate the deleterious dfects of the new aft& and restor;rtio91 r9t the genie balance such that resistant gem)types arc rquaP$y fhl as swxtrptibltrs E’VCBI iI1 insecticide-free el.lviToI1lDar[ltsl. ‘This iS exactly what has been shown to have hap pened in the case of diazmorr resistance in Luciliu.

gene plWdllCi:S are present in imaginal discs at the time of bristle formation in

&y-l

pupae”.

chanisms and Kop-1 gene products

by which interact

.W

in pro-

the asymmetry phenotype remain unlknown. 111Drlosophiiu, i%f~h is known to be invclved in cell di~~e~e~~~at~~~ and ceil fate through its cd adhesion functions

ducing

and interactions with other proteinsli. It is thus possible that the Rap-l product also affects cell decision-making processes via altered cell adhesion functions, which

arr subsi:qcsrn:8y ameli0~tIrtl via imterachim with the Scl product’“. Further investigations

should resolve this issue. The re%ev;mce ol this intensive series

of experinmcmts to the evolution of deval0panr~laU stabilily is mot trivial. It has shown that stability and asymmetry ra1ced by a SmanPnumber of

can be influgwes

of Illiljor

tBffccl, each subject to substantial selecUitrrapressure. i+ hypothesis that is SOmPwhat Iw~ nebulous than those involving genoane-wide processes. It also provides

direc.*t evidence for a relationship between stability and fitness. As it is likelv that these mechanisms are lliglaly spec”ific to the model system cxam~ined, the resu%ts thus reinforce

the idea that

stability

is both

taxou- a11d cInalacltlr_sppcific. Therefore, aPtempts to generalize patterns and mechanisms of stability acr0ss taxa and charactcrs

may well be counter-procluctive. Firl;rlly this work highhghts the need to integrate ?cologica%, evohdionary and de-

velopmental genetics in any attem%H PaJ understand a topic as r~,mplcx as drvelopmcntal stability. e ~~llW~~JiJW~(? Ci~?W,r:t~ti~Jl~

~~iO/O~~

c:sM~L)icksionolimmrokg: GPOB0.YI m. Cun/wm A1(7-3;0l.Atrslralrtr (g.c~lo,krOcnrtr.csiro.rr~~)

.!.dXN~~tO~?‘.

IlOt h’UiiSSC’(~: II
by

and by t

mental degradation, and enforcement

of laws

would

a

deal with the most obvious problems, at Icast in some nations. The greatest successes have irmvojved issues such as local and regional pollution, in which the signals are strong, cause and effect is clear, and hrncc the potential for remc4i .j is great. A key ta9why these work, when they do, is that cause and effect are closely linked in space and time; it is thus relatively easy to see the consequences of inactiolh. and the path to amelioration. For many of the most egregicrus [JKtPbPemrs, the

howevt?r, Pass

of

such

xi

#khal

biudiversity,

clranije

the causes

md

are

diffuse, the effects indirect and the signals slow to make themselves apparent. Mismatches of scale es:;ce lem, making local ac’i;on al issues. in the face of the e about the costs and benefits of remedial covery become

actions, the steps to reless clear and ilntermi-

nably postponed, perhaps to the point that irreversible changes o~:cur in the structure

interfere

with natural

processes

of

succession and change, and would ultimately weaken the ability of those systems to rem?‘2 virai in the face of a changing environment. Instead, ~~~a~erne~t must seek to identify what features of ecological systems are most vaQued by humans. and find ways to preserve them bj reinforcing their resilience in the face of stresses. This challenge is made more difficult by the recognition that there is no single yardstick for valuation. Different individua?s have difierent yardsticks: in1 equitab!c decision prc9cess lnlrst KW9jiaW this ambiguity, and lint1 ways to rep~s~nI and balailce these diverse !~rsp~“ctivcs and to resolve conflicts. To address issues 0f this sort, a convocation was held at Princeton University, NJ, LEA last autumn, under the sponsorol the Princeton ~~vjr~~~~e~ta~ Instiand supported by Princeton University and Edmund A. Stanley, dwell-known Maryland environmentalist. %tbrought together scientists. human

tioaiers from a broad spec

and functioning of natural as well as managed systems. This dilemma increases the

the ways in which humans value their environment, in order to provide a frame-

urgency of quantifying the services that these systems provide to humans and the essential nature of protecting these systems hefore the extent of degradation has

work Par sustaining the features that are mtast bigbiy vak 71’. Hiodiversity Provides a case ill pc%at.

ckosed the door to recovery. One approach is lo take a total preser-

i~portawce system

vationiist view of the environment; that is, ta, insist on saving all the parts in the spirit IPI enlligbtened tinkering. But this Is nei-

understanding t&e dynamics of ecolo$cal systems. Preservation of the most claarisnnatic species can be justified wit~~~~~t ref-

ther politically practical nor sound management, in that ecological systems are

iicrence to services; there is also the &sopC, of course, that in saving tlrese, one Saves

dynamic

assemblages

landscapes

diversity.

Some species will inevitably

of ever-changing be

hCk~.;t;lWii~llJ

lkdivel-sity

for

services,

Moreover,

and

Pa).%. 4rltY

it%

the maintenance

is intimately

other

0P”ecoBinked wit!l

species

the importalIce

as well.

of som ces of