Novttates PUBLISHED by the AMERICAN MUSEUM of NATURAL HISTORY CENTRAL PARK WEST at 79TH STREET, NEW YORK, N.Y

AMERICAN MUSEUM Novttates PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, N.Y. 10024 Number 2939, 25 pp., 15 figs., 4 tables April 26, 1989

Evolution of Extreme Sexual Dimorphisms: Structural and Behavioral Convergence Among Broad-Headed Male Drosophilidae (Diptera)

DAVID GRIMALDI1 AND GENE FENSTER2

ABSTRACT Males with broad heads (hypercephaly) have ative growth was compared among the droso- arisen 21-24 times in various taxa of flies; 11 in- philids using regressions oflog,0 measurements of stances are in the Drosophilidae. Details of the head width on thorax length. Hypercephaly is a morphological modification ofthe male head vary consequence, despite the manner of modification, among the hypercephalic taxa, with drosophilids of accelerated growth of certain head sclerites, possessing all the types of modifications seen in which is manifested in Zygothrica as well by ab- other hypercephalic flies. Cephalic modifications normal growth ofsetae. Predisplacement ofgrowth include distension of the eyes and/or various cra- onset and hypermorphosis rarely contribute to the nial sclerites or plates (i.e., facial, parafacial, fron- sexual dimorphism. Only Zygothrica latipanops to-orbital, occipital plates, and the frontal vitta males were found to occur in two discrete classes and ocellar triangle). Reproductive behavior ofhy- (a and #, or extremely and moderately hyperce- percephalic drosophilids and their close relatives phalic males). A phylogenetic analysis of the apo- is described for some species and reviewed for morphies associated with hypercephaly provided others. Measurements are given on eye and head the following hypothesis: in order from the most shapes and comparisons are made ofapproximate to least inclusive feature is territoriality, a frontal optical resolutions. Associated with hypercephaly approach prior to male fighting, head butting, and is aggressive male behavior (head butting and then, at the apical node, are hypercephaly with its jousting) and vision enhanced for either binocu- associated optical features and jousting. No re- larity (in the pedunculate eye forms) or frontal course is made to explanations ofnatural or sexual resolution (those species with conical eyes). Rel- selection regarding origins of correlated traits. INTRODUCTION In the delightful book, "The Natural His- seem to need so many aids to success in cop- tory of Flies," Oldroyd (1964) said of the ulation-spotted wings and male display, small, black dung flies, the Sepsidae (pp. 175- aphrodisiac odor by the females, special male 176) that "it is curious that these little flies clasping organs-when other flies manage ' Assistant Curator, Department of Entomology, American Museum of Natural History. 2 Department of Biology, Queens College of the City University of New York, Flushing, New York.

TABLE 1 Hypercephalic Diptera Number of Taxa v :... appear- ances Imm a 1 Diopsidae (all genera except Centrioncus) 11 Drosophilidae Chymomyza spp. j>.,8X Drosophila (Drosophila) heteroneura Drosophila (Hirtodrosophila) caputudis Mulgravea asiatica Drosophila (Hirtodrosophila) chandleri Zygothrica spp. 1 Micropezidae L Anaeropsis guttipennis ,-kS t.., 1-2 Otitidae _ antenna < Plagiocephalus spp. Ophthalmoptera spp. 2 Periscelididae Sphyroperiscelis spp. Diopsosoma spp. t t9 d 2-4 Platystomatidae Platystomatinae: :a--Fig. 1. Examples$,,.of hypercephalic.. Diptera. a- Achias spp. c,"@''Richardia...... telescopica; a, female;kb, male feeding Achiosoma spp. on monkey droppings, wings are outstretched Brea spp. (Barro Colorado Island, Panama [BCI]); c, male Laglaizia spp. head, frontal view. d, Teleopsis sp. male (female Scholastinae: has slightly shorter eye stalks). a, c, and d are to Asyntona the same scale. Note differences in position of the Mesoctenia antennae. Pterogenia Trigonosoma Zygaenula without any of these." It is indeed enigmatic 2 Richardiidae why any bizarre sexual dimorphism should Richardia telescopica come to be, and the frequency with which Richardia spp. (nr. annulata) this question is asked is usually a direct re- 2 Tephritidae flection ofhow bizarre is the feature in ques- Pelmatops ichneumonea tion. Themara lunifera Among the most intriguing sexual modifications in insects is male hypercephaly (fig. 1). The well-known example is seen in the publ.) and a eurytomid (Yoshimoto and Gib- Diopsidae, but in most diopsids the male eye- son, 1979); the instances of stalk-eyed Het- stalks are only slightly longer, per unit ofbody eroptera (e.g., Stonedahl, 1986) are not sexual size, than those of the female (Eggers, 1915; dimorphisms. Frey, 1928; Deschamps, 1957; Shillito, 1971; Numerous explanations have accounted for Burkhardt and De la Motte, 1985). The di- the presence of eyestalks, mostly because of morphism is much more obvious in seven the attention directed to the Diopsidae. Vir- other families of flies, as seen, for example, tually all ofthe explanations have been based in Richardia telescopica (Richardiidae) (fig. on proximate-mechanistic factors, particu- 1). Hypercephaly has arisen at least 21 times larly sexual selection. Burkhardt and De la in the Diptera (table 1) and several more times Motte (1985) suggested, based on previous in other insects: twice in the Hymenoptera, optical studies (Burkhardt and De la Motte, in an undescribed chalcid (E. E. Grissell, un- 1983; De la Motte and Burkhardt, 1983), that 1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 3 the eyestalks of Diopsidae impart an en- and is purely comparative, serving to expose hanced ability to size up opponents and mates, convergent patterns of hypercephaly and as- and at distances farther than are possible for sociated derived traits. Studying this trait in "normal"-headed individuals. The "size-up" Drosophilidae has the major advantage of hypothesis appears to have first been used by male hypercephaly having arisen more often McAlpine (1979) for Achias (Platystomati- in this family than in any other fly taxon. dae), but in a slightly different context. He Also, some phylogenetic work has been done suggested that two fighting males of Achias on the family (Grimaldi, 1986a; 1987a, meet with heads almost touching so as to 1987b; 1988), and a great deal is known about accurately determine the opponents' size. The the general biology of Drosophila. males thereby avoid unnecessary confrontations and thus injury (little mention was made by McAlpine of long-distance optical reso- ACKNOWLEDGMENTS lution and binocularity). McAlpine's hypothesis was espoused by Burla (1988) who ob- Many people contributed to this study and served rival males of Zygothrica dispar to for their help we are extremely appreciative. freeze head-on before an encounter either Quentin Wheeler and Toby Schuh provided ended in retreat or escalated into contact. In the use of micrometers, Ken Kaneshiro al- trying to account for the hypercephalic males lowed us to use the photos of the fighting of Drosophila heteroneura and their "ram- Hawaiian Drosophila, and Rob DeSalle and ming" behavior, Spieth (1981) suggested a Marshall Wheeler provided series of Hawai- sequence ofnatural and then sexual selection: ian Drosophila and Thyreocephala, respec- bird predation [somehow] selected for a tively. John Jaenike provided a series of the frontward approach of males and for ram- eyeless Drosophila recens. While D. G. was ming, and intermale competition resulted in in Panama, Steve Redhead helped with the head shape. Intrasexual selection, then, regressions, and Phil DeVries was as expert is the most common causal explanation of a field companion as is possible. Hampton male hypercephaly. Templeton (1977), how- Carson (University of Hawaii), Hans Burla ever, proposed that the broad head of Dro- (University of Zurich), Dietrich Burkhardt sophila heteroneura is a species-specific iden- (University of Regensburg), and David K. tification signal that aids females in choosing McAlpine (Australian Museum, Sydney) a mate (intersexual selection). In their most kindly read the manuscript and provided recent paper, Burkhardt and De la Motte critical comments. While at Cornell D. G. (1989) did a female choice experiment, which was supported by a NSF Doctoral Disserta- actually showed that the males of Cyrtodiop- tion Improvement Grant, NSF Grant BSR sis whitei with the broadest heads were fa- 8315457 to Quentin Wheeler, and an award vored by females. These authors elsewhere from the Cornell University Bailey Horto- (Burkardt and De la Motte, 1987) hypothe- rium (which funded travel to Peru). sized a sequence of several selection pressures, within and among sexes and species, MATERIALS AND METHODS that act upon diopsid mating repertoires. Fi- nally, Feijen (1984) wrote (p. 80): "A strong Most flies measured in this study were crit- argument against the selectional importance ical point-dried using absolute ethanol. ofeyestalks for binocular vision is in the large Pinned specimens were selected from various interspecific variation in the ratio eyespan/ series where there was minimal collapse of length of body." That is, if the role of bin- the cuticle. Scanning electron microscopy ocular vision is supposedly very finely adapt- used 10 kV beam current and gold-palladium ed to reproductive behavior, why is there so sputter coating. Techniques for observing fly much intra- and inter-specific variation in the behavior, especially Zygothrica, are provided trait? elsewhere (Grimaldi, 1987b). Morphological Many ofthe above arguments are intuitive- terms for parts ofthe cranium and other tag- ly reasonable and are not inconsistent with mata follow McAlpine (1981) and are pre- the observations. The approach here, how- sented in figure 2. ever, is devoid of selectionist explanations, Pinned specimens were measured in two 4 AMERICAN MUSEUM NOVITATES NO. 2939

-verticals- \~~~~ ~ ~--lg~~~~ __-- postverticals ---_ " ocellar triangle 0 ~ ~ ~ post re~~~clinate median occipital A--A ant reclinate s t II - f ialOStproclinatecleite- / plante ritl occipital scleritef-.J.-.

j ~~~~~~tentorial pt- carina ~~occipital foramen ~~~::~-fcilsclerite postgena----.....?.. .

Fig. 2. Frontal and ventral views of a generalized head of Drosophilidae. Terminology follows McAlpine (1981). ways. One was a Wild M-5 stereoscope with has been studied in insects, there is good cor- a camera lucida, with the image focused onto respondence between optically and behav- the surface of a digitizing tablet (Zeiss). Since iorally measured resolution (e.g., Bauer, the digitizing tablet's measurement error was 1985). about ± 0.001 mm, virtually all error was Eye curvature was measured by drawing due to positioning ofthe specimen and move- with a camera lucida at 50 x the outside mar- ment of the tablet cursor. Also used was a gin ofthe eye and head, as seen from a dorsal precision stage micrometer. Here, too, error view. The dorsal view was standardized to was due almost entirely to the positioning of approximate the position of a drosophilid the specimen. Thorax length (distance from head when held in a natural, live posture; this the anterior margin of the notum to the apex position was taken as the dorsal view that of the scutellum) was used as the most reli- maximized head length. Thus, one visual axis able and convenient measurement of body was measured, which was a plane approxi- size. mately horizontal to the substrate and lon- Since fly eyes are generally of the neural gitudinal to the long axis of the body in a superposition type, and thus have a single standing fly. Radius of the curvature was focal point, fairly simple methods can be used measured by comparing with a compass the to compare estimated optical properties such curve that best fit the outline. The radial length as resolution and binocularity (Snyder, 1979). was then measured on paper using the digi- Basically, resolution (R, the ability to distin- tizing tablet. For some eyes there were two guish two objects which are close together) main axes of curvature: a frontal one and a can be measured as r/D, where r is the radius smaller, posterolateral one (fig. 3a), desig- ofeye curvature (in ,lm) and D is the diameter nated as r and rl, respectively. Facet diam- ofthe eye facets in the plane ofthe measured eters were measured at 150-312 x (depend- radius (in ,um). This estimate does not take ing on size of the specimen) using scanning into account differences in optical abilities electron micrographs (fig. 3b). among species based on spectral sensitivity (detection of photons), binocularity, differ- THE FLIES ences in resolving power due to variation in Although not all species of hypercephalic ommatidia number, or, simply, how much drosophilids are represented in the scanning light there is in the fly's habitat. Estimates of electron micrographs in figure 4, most of the resolving power and other physical capabil- head structural variation seen in the family ities must eventually be tested with behav- is illustrated. Below are descriptions of the ioral assays, but such are well beyond the relevent behaviors and morphology for the means and efforts here. Fortunately, where it five main taxa ofhypercephalic drosophilids. 1 989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 5

Chymomyza Most ofthe following account comes from Grimaldi (1986a). Five species have hypercephalic males: Chymomyza microdiopsis (the most modified), C. exophthalma, C. diatropa, C. jamaicensis, and C. albitarsis. All belong to the aldrichii species group, which is mostly Neotropical in distribution. The first two species belong to one clade, and the re- maining three belong to another. Portions of each clade are partly distinguished by the manner in which crania are modified. Chy- R: r/d A momyza congregate at their oviposition sites on injured tree trunks, and the males usually outnumber the females there by four- to fiv- efold. Grimaldi (1 986a) provided data on relative head size in three of the hypercephalic species and in four species unmodified or slightly modified for the trait; the data are reviewed later in this paper. Widths of the face, the parafacial plates, and fronto-orbital plates have expanded in C. microdiopsis and C. exophthalma, but the eyes remain relatively unmodified in size and shape. In the other clade the eyes are slightly distended laterally, and the dorsal portion of the fronto- orbital plates has expanded, but the face and parafacial plates are virtually unmodified in width. Courtship for the aldrichii species group 100,um has never been observed. Only Chymomyza Fig. 3. Measurements used for comparing sev- amoena, a member ofanother species group, eral optical parameters in drosophilids. A, dorsal has been closely examined (Sturtevant, 1921; view of a hypercephalic male Zygothrica head. r = radius of curvature of frontal region of the eye, Spieth, 1952; Grimaldi, unpubl.). Male dis- r' = radius ofthe lateral region, x = origin ofcircle play and agonistic behavior has been ob- to which r belongs. B, scanning electron micro- served for C. exophthalma in Peru (Grimaldi, graph of frontal region of male Zygothrica tam- 1986a) and for C. diatropa in Panama (Gri- bopata eye, showing the measurement for facet maldi, unpubl.). In both species, the males size. 0 and 0' are the angles circumscribed by their rapidly zig-zag about on the bark while re- respective radii (these values not measured in this peatedly extending the wings and forelegs. study, but are used in computing interommatidial The wing and leg movements become more angles). exaggerated as males orient toward and approach each other. Fighting males face off copulation, as based on the observations of about one-half a body length apart and ex- C. amoena. Male Chymomyza are probably tend their forelegs while raising the body (fig. territorial since they congregate at specific sites Sa). The forelegs, particularly the tarsi, are but occupy smaller sites therein, frequently lashed against those ofthe opponent. Butting display, and fight with each other. with the head to the head and body of the opponent has never been seen in Chymo- myza. Apparently, the ventral rows of fem- Drosophila (Hirtodrosophila) oral spines in males is related not to the type Drosophila (H.) caputudis and D. (H.) of fighting behavior, but to courtship and chandleri are very closely related, and like 6 AMERICAN MUSEUM NOVITATES NO. 2939

Fig. 4. Scanning electron micrographs (frontal views) of some male Drosophilidae, all to the same scale; all except Zygothrica vittinubila (upper right) are hypercephalic. Left, top to bottom: Drosophila (D.) heteroneura, Drosophila (Hirtodrosophila) caputudis, Chymomyza diatropa, Chymomyza microdiopsis, Mulgravea asiatica. Right, top to bottom: Zygothrica vittinubila, Z. tambopata, Z. pilipes, Z. dispar, Z. latipanops, Z. exuberans. 1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 7

\ I 1 mm J \ z~~~~m ;~~~~~~;1~

AL ~ ~ ~ ~

Fig. 5. Habits of some hypercephalic Drosophilidae. a, Chymomyza exophthalma males slashing with their forelegs. They were observed on the cut end ofa tree trunk (BCI, Panama). b and c, Zygothrica. b, arrows indicate positions of four Z. prodispar males under the pileus of a mushroom; three of the males are on the edge surveying outward. The small, dark individuals are Z. virgatinigra. c, three Z. prodispar'>4males under the pileus in b. During most of the day the males are quiescent and tolerate each other (b,c: BCI, Panama). d, fighting males of Drosophila silvestris in the characteristic rearing stance. e, fighting (jousting) males of Drosophila heteroneura (photos d and e by K. Y. Kaneshiro). 8 AMERICAN MUSEUM NOVITATES NO. 2939 most of the hypercephalic drosophilids have the Hawaiian "Drosophila" should be noted. only recently been described (Grimaldi, Because of the bare eyes and lack of a facial 1 986b; 1988). Nothing is known oftheir hab- carina, many ofthe endemic Hawaiian species its, and only 16 specimens from peninsular would be plesiomorphic with respect to Dro- Malaysia are known for D. caputudis and three sophila sensu stricto according to a recent specimens from Sri Lanka for D. chandleri. phylogenetic hypothesis (Grimaldi, 1987a). Close inspection at fungi in these regions, Male D. heteroneura have all of the major particularly of fleshy, white, bracket forms cranial sclerites broadened with respect to would probably reveal the habits of the two those of D. silvestris: the facial sclerite, para- species. Almost all species in the subgenus facial plates, frontal vitta, fronto-orbital Hirtodrosophila and their close relatives con- plates, and the occipital sclerites are distend- gregate at such sites (Grimaldi, 1987b). The ed. The ocellar triangle, median occipital male heads of both species show remarkable sclerite, and the eyes contribute little to head convergence with that of Chymomyza ja- shape modification. Males of the planitibia maicensis and C. diatropa: the occipital scler- subgroup species are very aggressive and ites and the dorsal (but not the facial) portion highly territorial (Spieth, 1982, 1984). The of the fronto-orbital plates are laterally ex- darkly patterned wings are repeatedly sem- panded, the eyes are slightly distended (due aphored in both species, but vigorously so in mostly to the dorsal expansion-the distance the presence of females and while the fly is between the ventral margins of the eyes is faced toward another male. Fighting males unmodified), and the face is almost unmod- ofD. heteroneura slash with their forelegs and ified in width. All four species also have a head butt against the head and body of their dark brown band on the oral margin of the opponent (fig. 5e). This species has appar- face, which may be related to face-offbehav- ently lost the habit of fighting males raising ior in males and perhaps affect visual fixa- the front end ofthe body (i.e., in D. silvestris, tion. see fig. 5d), with one of them eventually de- pressing the body of the other. Males of D. Drosophila (Drosophila) heteroneura that joust (where the heads are in direct contact and there is pushing back Much has been studied about the hyper- and forth) may stay in contact for several cephalic species Drosophila (D.) heteroneura minutes (Spieth, 1981). In fact, during the and its close relatives in the planitibia species joust, the stout palpal setae found in the males group, particularly D. silvestris. The picture- lock into each other. Spieth mentioned (1984) winged group of Hawaiian Drosophila is en- that D. heteroneura is "the most pugnacious demic to that region and D. heteroneura and species of the subgroup." He also indicated D. silvestris are found only in rain forest on that head butting is synapomorphic for D. the big island of Hawaii. They breed in de- heteroneura and D. silvestris, since fighting caying bark of several arborescent, under- males of D. silvestris also butt heads, albeit story lobeliads, but males will form a lek, as briefly. do many of the planitibia subgroup species, at a large tree fern with each of them de- Mulgravea fending a leaflet (Conant, 1978). Drosophila heteroneura and D. silvestris are probably sis- This genus includes the hypercephalic ter species, as based on electrophoretic data species M. asiatica (originally as Lissoce- (Craddock and Johnson, 1979; Sene and Car- phala, then Thyreocephala). The species is a son, 1977), DNA hybridization (Hunt and distinctively patterned, tiny fly found in Carson, 1983), polytene chromosome inver- Amami, the Ryukus, Formosa, Burma, Ma- sions (Carson, 1971), chromosomal location laya, and Java. Despite its widespread dis- of a middle-repetitive DNA sequence (Hunt tribution, the sexual behavior and other hab- et al., 1984), and sexual behavior (Spieth, its have escaped notice. Its closest relatives, 1981, 1982), but these results are not con- sensu Okada (1985), are the Papuan species gruent with Kaneshiro's (1976) scheme. An M. bimaculata and M. parasiatica. alternative taxonomic placement of some of Widening of the fronto-orbital plates, the 1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 9 parafacial plates, facial sclerite, occipital sal portion of each fronto-orbital plate and sclerites, and even a modest extension of the to the occipital sclerites, which have pushed frontal surface ofthe eye all contribute to the the eyes anterolaterad. Displacement of the extreme hypercephaly of these males. The eye from the plesiomorphic position has re- frontal vitta and ocellar triangle are virtually sulted in a broad anterior eye surface and a unmodified in width. Okada (1965) com- tapered apex. The ocellar triangle and face pared the dorsal aspect of male and female are slightly expanded to varying degrees in a M. asiatica heads using a D'Arcy Thompson few species. Bristowe (1924) was the first to transformation grid, which provided a visual report on the sexual behavior of Zygothrica; portrayal of the amount of expansion con- his anecdotal report likened the jousting of tributed by the fronto-orbital plates. Z. dispar males to that of rutting bulls. Only recently have further, detailed observations Zygothrica been made on Zygothrica behavior (Grimal- Fifteen species belonging to this large, pre- di, 1987b; Burla, 1988). Males ofmost species, dominantly Neotropical lineage are hyper- but particularly the hypercephalic species, ac- cephalic as males, and in a manner unlike tively defend sites on fungal sporophores. that found in the other drosophilids. Hyper- Most activity occurs during the morning and cephaly has appeared six times according to evening; the flies are quiescent for most of the recent, phylogenetic analysis (Grimaldi, the day (e.g., fig. Sc). Confronting males first 1987b) and each time in clade B. In clade turn to face each other, from a distance of B.1, or the dispar species subgroup, hyper- about 3-4 cm in Z. prodispar and Z. dispar. cephaly has appeared three times: in exuber- They then rush at each other while flicking ans + dispar + prodispar (these have among out the wings one to several times and rapidly the most bizarre heads in the genus), in Z. vibrating them. During vibration the wing dimidiata, and in Z. dissimulata (which have blade surface is usually held vertical to the moderately broadened heads). Clade B.2, the ground, so that the broad surface is presented aldrichii subgroup, has two lineages of hy- to the opponent. Three hypercephalic species percephalic flies: pilipes + radialis, and tam- have been examined so far, but many more bopata + microeristes. Lastly, in clade B.3, of them and their close, nonhypercephalic the caudata subgroup, hypercephaly appears relatives need to be studied. When fighting, just once, involving aliucapa + caputrichia hypercephalic males face off at about one + laticeps + latipaps + latipanops (the last head-length's distance while rapidly vibrat- species has extremely hypercephalic males, ing the wings, and they then may lunge head- see below). All of the species aggregate at to-head and appear to push each other back mostly white, imbricate bracket fungi (figs. and forth (jousting) for up to one minute. Sb, c). At the rendezvous site they feed, court, Actually, Burla (1988) found in Z. disparthat fight, and mate, but they breed mostly in during jousting the male heads are very flowers. slightly separated and rarely touch. He also Figure 4 shows an apparently extensive found that territorial residents were the most morphocline in head shape for Zygothrica. successful males in encounters, and these There are actually slight differences among males also had substantially wider heads than the species subgroups in the extent of mod- the intruders. Unquantified observations of ification-ofcertain cranial sclerites, thus sup- Z. prodispar and Z. tambopata corroborate porting the previous hypothesis that hyper- this finding. Large, very hypercephalic males cephaly in the genus is synapomorphic at of Z. prodispar were found to be particularly several levels and convergent at other levels. active and aggressive. Burla also reported that Nonetheless, the Bauiplan of Zygothrica hy- Z. dispar males form temporary leks. How- percephaly is nearly unique for the Diptera ever, at least the other two Zygothrica men- and shares a gross similarity only with the tioned above are simply territorial since the pattern in the Papuan genus Asyntona (Pla- sites include about as many females as males tystomatidae) and some species ofRichardia and because the flies feed on the fungal sur- (Richardiidae). Lateral distension ofthe head face ("resource defense polygamy," sensu in Zygothrica is due to expansion ofthe dor- Emlen and Oring, 1977). 10 AMERICAN MUSEUM NOVITATES NO. 2939

TABLE 2 TABLE 3 Mean Facet Diameters (Mm) of Hypercephalic Optical Resolution Comparisons for Male Drosophilidae Drosophilidae Acute Ventral/ R r, r,, zone dorsal Apical (=r/d) RI gm ,um Chymomyza microdiopsis 20.4 14.7 15.6 *Chymomyza amoena 23.1 - 420 - Chymomyza diatropa 18.2 15.4 15.4 Chymomyza diatropa 33.6 14.1 612 218 Drosophila caputudis 30.0 24.0 24.0 Chymomyza microdiopsis 17.9 14.4 366 224 Mulgravea asiatica 16.0 11.2 14.2 Drosophila caputudis 16.8 9.3 505 223 Zygothrica prodispar 19.0 19.0 25.2 Mulgravea asiatica 26.2 9.8 420 140 Zygothrica pilipes 14.7 14.1 14.1 *Zygothrica orbitalis 18.0 - 338 - Zygothrica pilipes 53.1 12.1 780 170 Zygothrica prodispar 37.6 4.8 700 120 OPTICAL COMPARISONS * Species unmodified for hypercephaly. r = mean radius ofeye curvature (frontal region), d = Tables 2 and 3 present data on, respec- mean facet diameter from various regions ofeye; R1 and tively, facet diameters (in ,um) and estimated ri are resolution and radius measurements for lateral optical resolution (as measured per equation region of eye. given in the Materials and Methods section). The facet diameters of Chymomyza amoena, light-gathering ability (sensitivity) of a facet Mulgravea sp., and Zygothrica orbitalis (Snyder, 1979), it is not surprising that species (species unmodified for hypercephaly) were of Zygothrica congregate at white fungi even not measured; the resolution values in table though brown-colored forms are more com- 3 for these species were calculated based on mon on the tropical forest floor. facet measurements oftheir closest relatives. Zygothrica appears to have the best frontal Instead of "fovea," the term "acute zone" resolution, which was estimated at generally seems most proper since the eye region of twice as acute as that of other hypercephalic highest resolution is not a single, discrete species. It should be noted that, on average, point, but an area or areas grading into the males of Z. pilipes had broader heads than remainder ofthe eye (Land and Eckert, 1985). those of Z. prodispar, but in the latter species Although the acute zone was not measured, the range is much greater (see section on al- which is generally done in degrees from the lometry). Chymomyza diatropa males have eye equator (Land and Eckert, 1985), in some broad anterior eye surfaces, and subsequently drosophilids this region was obviously where this species ranked third among the nine for there was a round cluster of large facets in which resolution was calculated. The thor- the frontal region. Land and Eckert (1985) ough work of Burkhardt and De la Motte found that the region of highest resolution (1983) showed that the span between eyes coincided with the area of largest facets in proportionally increases long-distance depth Calliphora erythrocephala (Diptera: Calli- perception in diopsids. It can safely be as- phoridae) (they measured resolution by map- sumed that, because the eyes are separated ping pseudopupil displacement onto a sphere). by at least three to four times that which is In the "acute zone," Drosophila caputudis had "'normal," diopsid-like species such as Mul- the largest facets, then Chymomyza micro- gravea asiatica and Chymomyza microdiop- diopsis, Zygothrica prodispar, Chymomyza sis are able to resolve images at depths of at diatropa, Mulgravea asiatica, and finally least three or four times that which their un- Zygothrica pilipes. This order is opposite the modified relatives can perceive. rank order (from highest to lowest) of mea- In the hypercephalic species for which an surements in r (radius of curvature of the additional, lateral curve was fitted onto the frontal region ofthe eye). Generally, then, the eye surface, the radius of this curve was al- eyes with the broadest frontal surfaces (es- ways much smaller than the radius for the pecially Zygothrica) had the smaller facet di- frontal region. In Zygothrica, because oftheir ameters in this region. Given that there is a apically pointed eyes, the lateral curve of the direct relationship between diameter and eye was especially minute (about one-sixth 1 989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE I1I of the frontal). Also in Zygothrica, the facets at the tip of the eye are spaced far apart, and even lost in Z. exuberans and extremely hy- C percephalic males of Z. dispar. Thus, the lat- ..0,' eral portion of the hypercephalic eyes must have much less resolution than the frontal region. Despite the lateral impairment, hy- C ,, percephalic males generally have the tips of a)~~~~~~~~~A the eyes extended beyond the lateral surfaces @~ ~~~~~~~,0, of the thorax, and so these flies should have a rearward, albeit limited, perspective. The extent of differences in resolution among individuals of Z. prodispar is shown in figure 6. A positive, highly significant (p 0.3- < .01) relationship exists between head width and the radius of eye curvature ofthe frontal region, with values ranging between 0.29 and 1.09 mm. This variation may be related to a threefold difference in resolving power among 1.0 1.5 2.0 2.5 the smallest and largest males ofZ. prodispar, Head width (mm) as well as other species such as Z. dispar which Fig. 6. Relationship between head width and have such disparate variation in head size. radius of eye curvature (r, in mm) of the frontal Higher resolving power and better depth per- region in males ofZygothrica prodispar. The range ception could probably be translated into an in variation shown here is the maximum found increased ability of hypercephalic males to among specimens from a single collection taken distinguish distant objects, patterns, and mo- in Panama, and is about as great as that from all tion. Such an ability, no doubt, would be re- sites within the overall distribution of this highly lated to distinguishing conspecifics from oth- variable species. er flies, perhaps even distinguishing among conspecifics, and may reduce the time a territorial males takes to react to an intruder. quires extensive extrapolation beyond the endpoints of the regression. Such reasoning ALLOMETRY AND HEAD GROWTH led to several instances where biologically meaningless, negative y-intercepts were cal- Figure 7 shows four possible types of het- culated. Thus, here we present both HW (y) erochrony, or differential growth, between intercepts and, more properly, minimum HW species x and y. If the onset of head growth values. Given below for each group of hy- in x is later than in y, but growth rates are percephalic Drosophilidae is a discussion of equal, the result is hypermorphosis of x with the relative roles of predisplacement and ac- respect to y. Acceleration occurs when the celeration in head peramorphosis. slope of x is steeper than that of y, and may Chymomyza. Plots ofrelative head size for occur irrespective ofthe onset ofgrowth. So, species of this genus are provided in Gri- the parameters traditionally useful to com- maldi, 1986a. Slopes varied from +2.00 in pare among species are the y-intercepts and C. microdiopsis to about +0.60 in several slopes (see also, McKinney, 1988). Ifthe slope nonhypercephalic species, such as C. amoena ofthe allometric relationship within a species and C. procnemoides. The y-intercepts and is not significantly different from that ofclose minimum head width values varied little relatives, then body size is the main variable among the hypercephalic species, but did dif- explaining, in this case, head breadth (Lande, fer dramatically between these species and 1985). Even though y-intercepts (in this pa- the nonhypercephalic ones. Growth acceler- per, the axis for head width [HW]) are tra- ation accounts most for Chymomyza hyper- ditionally used in allometric analyses, it can cephaly. Although the trend is not significant be a misleading method because it often re- (p>-.06), the scatter plot suggested that males 12 AMERICAN MUSEUM NOVITATES NO. 2939

0 log10 Body Size rates equal x accelerated x accelerated x accelerated onset x later onset x later onsets equal onset x earlier (hypermorphosis) (acceleration f (acceleration) (acceleration * hypermorphosis) predisplacement) Fig. 7. Basic models of the differential (peramorphic) growth of x as compared to y and the terms used to describe each mode. of Chymomyza microdiopsis fall into two D. heteroneura, but there needs to be a greater groups based on relative head width. range in body size among the specimens to Drosophila (Hirtodrosophila). Little can be confirm this. said of D. caputudis because comparison to Mulgravea. Two species were measured, its closest known, nonhypercephalic relative, M. asiatica and an undescribed species in the D. (H.) yakushimana Okada (Grimaldi, genus closely related to asiatica that is not 1986b), has yet to be done. Only two males hypercephalic (fig. 8). r2 = 3.99 for males of of Drosophila chandleri are known, so this M. asiatica and is 0.75 for males and females species was not included in the regression of Mulgravea sp. and for the females of M. plot. In the event that sufficient material of asiatica. Obviously, the 2.50 y-intercept for these close relatives becomes available, then M. asiatica males compared to +0.40 for such measurements can be compared with Mulgravea sp. males and females is an arti- the data in figure 8 for D. caputudis. fact of extrapolation, and yields a predis- Drosophila heteroneura. Specimens of this placement ofapproximately 500 x! Based on species and D. silvestris were obtained mostly minimum y-values for each species, predis- from laboratory stocks and, as a result ofcon- placement may not account at all for M. asia- stant developmental regimes, little size dif- tica hypercephaly, but only acceleration. ference was found among individuals (un- Zygothrica. Burla (1954, 1955) was the first fortunately, at least D. heteroneura is quite to describe the allometry of male Zygothrica rare in the field, and wild individuals have heads. He compared HW and ThL among not been found for the last several years). No males of Z. dispar, Z. prodispar, Z. laticeps, significant differences (p > .05) were detected and Z. orbitalis (the last is not hypercephalic). within or between species for the overall Although these two studies showed that the regression (fig. 9), which may be a result of slope of the HW-ThL regression was highest the use of lab material or actually indicate for Z. prodispar, y-values have not been com- that accelerated growth is not involved in the pared. Perhaps the most intriguing result from hypercephaly. However, significant differ- Burla's studies was the quantification of a ences were found between species for the bimodal distribution of male Z. dispar head means ofboth HW and ThL. In both species, widths relative to thorax lengths. This feature males had significantly larger (p < .05) HW appears obvious to the trained eye, such that values than the females, while the variances males can be sorted into moderately (f-males) of HW and ThL were not significantly dif- and very broad-headed (a) individuals with- ferent (p > .05). Hypermorphosis seems to out measuring them. However, the presence account most for the hypercephaly of male ofbiphasic male allometry has not been cor- l1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 13

0 A

3.10 - . A

0 A

3.00 -

0 A 0 E A 0 -o 2.90 -

0a I.

2.80 -

2.7C -

I I I I I I I I 2.70 2.80 2.90 3.00 3.10

Thorax length, ,um log1o Fig. 8. Relative head sizes in Mulgravea spp. and in Drosophila caputudis (see text for discussion of regression parameters). In all regression figures the solid symbols are males and the empty ones are females. 14 AMERICAN MUSEUM NOVITATES NO. 2939

350

r 0 heter°oneu

0 &40[ E 0 0~~~~00

-c

I- 3.30- he, erofleur° 0= 0 U. ( si/yes'tris * *-O a) 320 sivestris9? 3.35 UO40 3.45 Thorax length,,um loglo Fig. 9. Relative head sizes in two species of Hawaiian Drosophila. roborated here for Z. dispar, nor found in nents analyses (PCA) on the covariance ma- any of the hypercephalic Zygothrica species trix of the males of each species were used to except for one. Sample sizes of the rarer test for the existence of a- and A-males. species should eventually be increased so as Spearman's rank correlation coefficients (r,) to more rigorously test for biphasic allome- indicated that there was little relationship be- try, but the preliminary indication is that the tween HW (y)-intercepts and minimum y trait will be rare in Zygothrica. In view, too, values for males in the aldrichii and dispar of the recent discovery of numerous new hy- subgroups. The rs for the caudata group (- percephalic species (Grimaldi, 1987b), com- 0.87) was strongly negative, and was calcu- prehensive data are presented here that com- lated with the division of Z. latipanops into pare Zygothrica head allometry. a- and f-males. The only other negative re- All of the statistical analyses used Version lationship was for aldrichii subgroup males 5 of SAS. Regressions were initially made of (-0.40). For each group rs was higher when log1O transformed values of HW on ThL for sexes were pooled as well as when all of the each sex of 15 species in Zygothrica. Sample Zygothrica species were included. Every at- sizes (N), y-intercepts and their standard tempt possible was made to include speci- errors, minimum y values, slopes and their mens representing the range in size for mea- standard errors, and r2 values are presented surements ofeach species; thus, with the lack in table 4. Comparisons were made between of correlation discussed above, it would ap- species, and between sexes in some cases, for pear that minimum y value, not y-intercept, slopes and minimum y-values. For Z. dispar, is most appropriate to estimate size at the Z. prodispar, and Z. microeristes, the males initiation of head growth in Zygothrica. All were divided into groups based on collecting regressions are displayed as scatterplots in locality, and locality regressions were com- figures 10-12. Allometric descriptions of the pared as a check for geographic variation in head for each of the three Zygothrica species allometry. Since no geographically distinct subgroups that have hypercephalic members groups were found, individuals were pooled are given below. where necessary from several collecting lo- The dispar Species Subgroup. Both Z. an- calities. ANOVAs and a posteriori multiple tedispar and Z. exuberans had sample sizes comparison tests examined for differences too low for statements to be made regarding among mean HW and ThL values within each their regressions, and they are presented in species group. T- tests and F-tests compared the plots in figure 1 Oc simply for visual com- the means and variances, respectively, of the parison. Zygothrica dispar (fig. 1Oa) and Z. sexes within each species. Principal compo- prodispar (fig. Ob) both had significant diff- 1 989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 15

TABLE 4 Regression Values for Zygothrica Species SE of Min. SE of Y-intercept intercept Y-value Slope slope r2 Males Male latipanops (N = 16) -2.189 3.120 1.729 0.954 0.190 A-male latipanops (N = 8) -13.293 8.850 1.46 5.162 2.710 0.165 B-male latipanops (N = 8) -8.810 2.053 3.26 3.721 0.626 0.620 caudata (N = 4) 0.305 0.866 3.10 0.878 0.265 0.845 latipaps (N = 3) -0.658 0.501 3.08 1.178 0.154 0.983 posthona (N = 5) -0.674 0.410 3.14 1.187 0.043 0.996 microeristes (N = 62) -2.063 0.445 2.95 1.678 0.146 0.686 pallida (N = 32) -0.388 2.88 1.099 0.954 pilipes (N = 9) -3.670 1.170 2.19 0.828 0.379 0.828 radialis (N = 37) -2.686 0.340 2.96 1.873 0.111 0.891 tambopata (N = 34) -2.981 0.414 2.97 1.962 0.134 0.869 antedispar (N = 4) 3.500 0.424 3.02 -0.152 0.136 0.387 dimidiate (N = 15) 0.833 0.978 2.96 0.178 0.317 0.795 dispar (N = 106) -6.528 0.480 2.94 3.177 0.157 0.798 exuberans (N = 6) -4.140 2.867 3.39 2.444 0.916 0.640 prodispar (N= 119) -3.898 0.396 2.89 2.284 0.128 0.730 heteroneura (N = 15) -0.613 0.424 3.40 1.191 0.124 0.876 silvestris (N = 12) 0.320 0.365 3.22 0.858 0.106 0.867 Females latipanops (N = 4) 1.195 0.612 3.22 0.401 0.184 0.703 latipaps (N = 4) -0.544 0.382 3.16 1.136 0.115 0.980 posthona (N = 7) 1.639 0.652 3.16 0.471 0.200 0.528 microeristes (N = 26) 0.044 0.196 2.95 0.965 0.064 0.905 pilipes (N = 5) -2.520 0.901 2.98 1.785 0.288 0.928 radialis (N = 17) 0.084 0.433 2.98 0.952 0.139 0.757 tambopata (N = 18) 0.271 0.374 2.98 0.887 0.120 0.775 antedispar (N = 2) 2.411 3.04 0.202 1.000 dimidiata (N = 16) 0.5 10 0.413 2.92 0.813 0.133 0.728 dispar (N = 33) 0.283 0.252 2.97 0.892 0.081 0.795 prodispar (N = 24) 0.491 0.359 2.95 0.820 0.116 0.696 heteroneura (N = 11) 0.012 0.456 3.27 0.966 0.133 0.853 silvestris (N = 11) 0.117 1.037 3.20 0.908 0.302 0.502 ences in the male and female regressions (p Slopes and intercepts of males were differ- < .05 for both slopes and intercepts). Growth ent among species (p < .05), but this was not acceleration appears to be the main factor in true for the pooled sexes and for females only. the hypercephaly of these two species. Zyg- Thus, a comparison of male regressions ex- othrica dimidiata and Z. antedispar, which cluding Z. antedispar and Z. exuberans did not have sexually dimorphic regressions, showed the slopes and intercepts to be dif- were also the two species of the group with ferent (p . .05). Zygothrica antedispar is the positive male y (HW)-intercepts. For Z. dis- member ofthis group studied here that is not par and Z. prodispar, mean HW was signif- hypercephalic, even though it is among the icantly larger in the males, while, as is true largest ofthe species. It is also the only mem- for most flies, mean ThL was larger in fe- ber that had a negative slope, though this males. Also interesting is the finding that these could be a result of small sample size. For are the only two species ofthe group for which mean HW, Z. exuberans and Z. antedispar there were significant differences in the vari- were at opposite extremes of the range, ance ofeither trait. In both species the males whereas they were indistinct for ThL and to- were more variable in HW than were females. gether separated from the other three species 16 AMERICAN MUSEUM NOVITATES NO. 2939

3.41- dispar

0000 0.*.S0 3.01 OS% a

0 a 0 E a4 prod/spar

-o 3.21-

;*0St~~~~c o 8 0 S,,j I

as1 (,beron"6

&4-

&2 - 0 .

dimidiato~ 5-0 --O-Cy- ao [ _ -ontedispor 0 C

2.92 300 Wo1 &is Thorax length,,jm log1o Fig. 10. Relative head sizes in five species of the Zygothrica dispar species subgroup. l1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 17

0 0~~~~~~~~~~~~~ E 3.40 Thora lengh,u lo1tipnoP9

V --~~~~po_- 0 Fig.4- l. Relative head sizes sp 3.20 inthre-d

3.15 3.25 3.35 Thorax length, ,um log1o Fig. 11. Relative head sizes in three species of the Zygothrica caudata species subgroup.

(Duncan's multiple range test). Zygothrica tercepts of the two male groups were signif- dispar and Z. prodispar males group apart icantly different (e.g., fig. 1 1). This is the only from Z. dimidiata based on HW even though one among four Zygothrica species analyzed all three species have similar ThL. The for which biphasic allometry was found. Not ANOVA indicated that females, in contrast surprisingly, this is the most modified in rel- to males, showed no significant differences ative head width among all Zygothrica among species in mean HW or ThL. species. In this subgroup, too, acceleration The caudata Species Subgroup. With the accounts for hypercephaly. exception of Z. latipanops, the sample sizes The aldrichii Species Subgroup. Zygothrica for this group are too small to have much pilipes, which had the lowest sample size in confidence in the regressions (fig. 11). Sig- the group, was the only species that had no nificant differences in the slope and intercepts allometric sexual dimorphism (for this were found between sexes of Z. latipanops species, females are more hypercephalic than and Z. posthona. Regression comparisons is found in any other Zygothrica). For all among species indicated no significant dif- species the male y-intercept was negative, and ferences when the sexes were pooled or for for Z. pilipes this was true for females as well. just the male regressions. However, signifi- Zygothrica pallida was the member of the cant differences were found for both the slopes group studied here that is not hypercephalic, and intercepts of the females! These differ- and it showed the same allometric relation- ences may be due to small sampling effects ship to other members of its group that the and perhaps as well to smaller female vari- nonhypercephalic species Z. antedispar ances. Zygothrica latipanops is similar to Z. showed to other members of the caudata disparand Z. prodisparin that males are much subgroup (fig. 12). Accelerated growth ofmale larger and more variable in HW than are fe- heads accounts for the sexual dimorphism in males, which are larger in ThL. Males of Z. this subgroup. latipanops were divided into two principal components, the major difference of which GENERAL GROWTH was primarily along the second principal CONSIDERATIONS component (for which ThL weights most [p Similarities are seen in the modification of < .05 for equal ThL means]). Slopes and in- head setae in some hypercephalic Zygothrica 18 AMERICAN MUSEUM NOVITATES NO. 2939

.20

.10 tambopaf . 0 0 0 0 go 0 J` 0 0 * o 0 000 00~~~~~~~~~% 0 00~~~~~ 3A .w a LI

0 0 microers/ses . 0 3 020 .0 % 0 0 0so 0 0 0 0 .0 0 .00 r0 . **~~~00 0 0 0 0 0 00 00 0 0 0 0* 00 0 0 E 2 -o *3_

I-0 0~~~~~ 0) 3 I 0.0. .90 0~~~~~~o c

000 0~~

Thorax length,,um log1o Fig. 12. Relative head sizes in five species of the Zygothrica aldrichii species subgroup. 1 989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 19

- PRO

--S

IV-)

P-

Fig. 13. Abnormal head growth in some drosophilids. a-c, Drosophila recens, unilateral eyeless mutant (a, lateral; b, frontal; c, posterior views). Setal abbreviations same as in fig. 14 plus the following: G, genal; PO, proclinate orbital; PRO, posterior reclinate orbital; S, supracervical; V, oral vibrissa. Note duplication and kinking of some setae in the same manner as for extremely hypercephalic Zygothrica (fig. 14). d, scanning electron micrograph of Zygothrica dispar male head (frontal view). Of nearly 5000 specimens examined for this species, this individual was the only one with asymmetrical eyes. Drosophilid eyes develop independently from separate anlage. The asymmetry is either rarely produced, rarely viable, or its rarity is due to a combination of both factors. and those Drosophila mutants that have var- of either side of the head is independent of ious degrees of eyelessness (ey). Three in- the other-e.g., fig. 1 3d). Ipsilateral to the lost stances of ey are known in Drosophila: D. or reduced eye is an arista that is lost or mal- melanogaster (reviewed in Lindsley and Grell, formed, but the base ofthe antenna, the face, 1968), D. pseudoobscura (Farmer, 1984), and and the contralateral portions ofthe head are D. recens (Jaenike, 1985) (fig. 13). For all rarely affected. The setae are sometimes du- three species a gradation of partial to com- plicated, and nearly always are stubby or pletely unilateral or bilateral eyelessness can crooked. occur. Proportional to the degree of eyeless- The smallest males of several hyperce- ness is the extent ofloss, duplication, and/or phalic Zygothrica have relatively normal se- malformation of the ipsilateral orbital and tae on the head and thorax. While no acros- vertical setae (this fact corroborates early an- tichal setal modifications occur in the lage studies which showed that development Drosophila ey mutants, there is an obvious 20 AMERICAN MUSEUM NOVITATES NO. 2939 and direct relation, within and among Zyg- probably is not biphasically allometric for othrica dispar, Z. exuberans, and Z. prodis- male hypercephaly, the subsequent discovery par, between the degree of hypercephaly and that Z. latipanops indeed is indicates that the size of postvertical, postocular, and ac- biphasic allometry in male secondary sexual rostichal setae (fig. 14). In addition, in the features extends across several orders of in- most hypercephalic individuals of Z. dispar sects. Numerous other hypercephalic Diptera and Z. microeristes, several of the verticals have yet to be tested. Biphasic allometry in and/or postverticals are crooked. In Z. lati- male horn size and shape occurs repeatedly panops (not figured), the most hypercephalic in various beetle taxa, including Ciidae, males have duplicated proclinate orbital and Leiodidae, Scarabaeidae, Staphylinidae, Te- dorsocentral setae. Thus, gross expansion of nebrionidae, and other families. Besides bee- a cephalic sclerite apparently accelerates the tle horns and wide fly heads, we are unaware growth of the setae that lie on it (during the of any studies on other orders where a male pupal stage) and, in extreme cases, the de- sexual character has been tested for a biphasic velopment of normal, straight setae is dis- distribution, so it is difficult to say exactly rupted. Perhaps a similar mechanism affects how widespread male biphasic allometry is. the hypermorphic interfacetal (eye) setulae in However, given the repeated appearance of Drosophila (H.) chandleri (see Grimaldi, the trait among at least some insects, one 1988) and the unrelated species in Diopso- must conclude that environmental factors, soma (Diptera: Periscelididae). Both ofthese such as differences in larval nutrition, have hypercephalic taxa have a patch oflong, stout, only minor involvement, and probably act in scaliform setulae in the middle of each eye, conjunction with some more influential, ge- which may be related to a particular envi- netic-developmental factors. The expression ronmental condition and manner of vision, ofthe trait is very similar to those exhibiting a result of cephalic hypermorphosis, or per- threshold effects, the mechanism ofwhich is haps a combination of both. These growth usually seen in physiological processes (e.g., patterns suggest the involvement ofa general enzymatic rates) but which we believe could inducer affecting particular areas of the head also be involved in morphogenesis. It is pos- and all structures within such regions, such sible that at least some structures are subject as has been hypothesized for color patterns to threshold effects during development, but in lepidopteran wings (Nijhout, 1986). due to the scale of measurement and error, Convergent patterns in drosophilid hyper- threshold effects are most likely to be de- cephaly illustrate that various sets of cranial tected in exaggerated features: the greater the sclerites are involved. For example, in all in- variance in the size and/or shape (as was found stances offronto-orbital plate widening there to be the case for the hypercephalic droso- is a widening of the occipital plates as well; philids), the more defined morphs become. likewise for the face in conjunction with the fronto-orbital plates. In only some instances ofeye distension are the parafacial plates also CONVERGENCE AND "ADAPTATION" distended. These patterns are no doubt a re- flection of the eye-antennal anlage structure Figure 15 is a phylogenetic hypothesis and growth (Ouweneel, 1970; Ransom, 1982), (cladogram) ofthe five drosophilid taxa where and they at least corroborate that the eye be- hypercephaly occurs, with several morpho- haves like and should have the same devel- logical and behavioral apomorphies added. opmental origin as the other cephalic sclerites The monophyly and relative relationships of (Butt, 1960). It might be of great benefit to these genera and of groups therein are sup- select and cross some hypercephalic and non- ported mostly on the basis of morphological hypercephalic drosophilids, and determine features different from those in the analysis. the genetic bases of head shape modifiers. Several aspects of the diagram require de- Unfortunately, most of the hypercephalic tailed discussion. Somewhat obvious is the drosophilids are either quite rare or are very fact that an altered visual field, either an im- demanding for laboratory culture. provement in frontal resolution (for apically Despite the fact that Zygothrica dispar tapered eyes) or binocularity (for the pedun- 1 989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 21

HEAD, DORSAL SURFACE PROFILE OF NOTUM

SMALL MALE

( '.

LARGE MALE exuberans

X, .. -,

SMALL MALE ;tes

i...... -, .,:. .. .-. jp. LARGE MALE Fig. 14. Head (dorsal surface) and notal setae (dorsal thorax in lateral view) in some hypercephalic Zygothrica. Shown are a large and small Z. dispar male, a large Z. exuberans male, and a large and small male of Z. microeristes. iv, inner vertical seta; ov, outer vertical seta; p, postocular seta; pv, postvertical seta. culate forms) is always associated with mod- but it appears that jousting by fighting males ification ofhead shape. The data are limited, is concomittant with hypercephaly. Studies 22 AMERICAN MUSEUM NOVITATES NO. 2939

clade A B OG B.2 B.3 OG eyes tapered, frontal resolution high eyes pedunculate, binocularity high IF T ~~~~~~~~~~~~~~~~~~~~~hypercephaly ? _ ? j ?_._ v jousting7 v § ? ? < ? * ? * head butting

______?-? confrontations: II I v ' initial face-off PI territoriality

Fig. 15. Phylogenetic hypothesis of various traits associated with male hypercephaly in several taxa of Drosophilidae. Not all of the features that distinguish between the various clades (e.g., Zygothrica B. 1, B.2, B.3) have been included. "OG" is the most closely related outgroup for each of the various taxa, and was used to polarize the state of each morphological and behavioral apomorphy. Apomorphic states are dark circles, plesiomorphic states are empty circles. Although the apomorphies at the right of the figure are convergent among most of the higher groups, they are defined as synapomorphies for the more terminal taxa on the basis of differences in structural and behavioral details. The relationships of Mulgravea and the Hawaiian Drosophila to the other taxa have yet to be detailed; ? indicates missing data, see text for discussion. on the very hypercephalic species Chymo- drosophila, which is closely related to the sub- myza microdiopsis and Mulgravea asiatica genus Hirtodrosophila, males are territorial would provide the best test ofthis prediction. but, in at least two Neotropical species ob- Males that fight by using the head very briefly served by Grimaldi, fighting males back into to butt the body or head of the opponent are each other and slash with the hind legs. more widespread in drosophilids than are Thus, there are apparently certain precon- jousting males, and such males are found ditions ("preadaptations," sensu Cuenot among the outgroup taxa. For example, the [1936] and ultimately others) associated with nonhypercephalic species Zygothrica orbi- the rise of male hypercephaly in the Dro- talis doesn't joust, but does use the head for sophilidae, and probably other flies as well: brief butting, and the situation is similar for territoriality, face-to-face confrontations, then Drosophila silvestris. Ofthe several species of head butting, and jousting. There is a general D. (Hirtodrosophila) that have been observed trend for the hypercephalic drosophilids to by Grimaldi, males behaved this way; but, be more aggressive than their unmodified rel- again, for Chymomyza and Mulgravea more atives; that is, engage in more confrontations. data are needed. For the three taxa that are Therefore, we interpret jousting to be just a known well enough, it appears that territo- prolonged bout ofhead-to-head butting, tak- riality and confrontations where males ini- ing place between aggressive individuals that tially face each other are traits even more are not prone to immediately back away in widespread than is head butting. In Myco- an encounter as are most nonhypercephalic 1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 23 flies. Thus, there are alternative explanations Kopfbreitenwachstum bei Zygothrica to such adaptationist ones as McAlpine's "size dispar (Drosophilidae, Diptera). Funf. up" hypothesis. We do admit that under- Jahrb. Schweiz. Gesell. Vererbung. 30: the evolution of this sexual dimor- 489-494. standing 1988. Lek behaviour in Brazilian Zygothrica phism may be enhanced by studies of selec- dispar (Drosophilidae). manuscript. tion and developmental mechanisms. For Butt, F. H. example, given the improved binocularity or 1960. Head development in the arthropods. resolution associated with hypercephaly, why Biol. Rev. 35: 43-91. arejust a few taxa hypercephalic? There could Carson, H. L. be insufficient selection pressure and/or ge- 1971. IX. Polytene chromosome relationships netic variation for hypercephaly in most in Hawaiian species of Drosophila. V. species of Drosophilidae. Perhaps selection Additions to the chromosomal phylog- for hypercephaly in some taxa imparts sub- eny ofthe picture-winged species. Stud. Gen., VI. Univ. Texas Publ. 7103: 184- stantial developmental consequences (e.g., 191. Carson and Teramoto, 1984), more severe Carson, H. L., and L. T. Teramoto than those discussed for Zygothrica? Such 1984. Artificial selection for a secondary sex- questions can only be posed now that the ual character in males ofDrosophila sil- descriptive and comparative basis has been vestris from Hawaii. Proc. Natl. Acad. established. Sci. 81: 3915-3917. Conant, P. 1978. Lek behavior and ecology of two sym- REFERENCES patric homosequential Hawaiian Dro- Bauer, T. sophila: Drosophila heteroneura and 1985. Different adaptation to visual hunting Drosophila silvestris. M.Sc. thesis, Uni- in three ground beetle species ofthe same versity of Hawaii, Honolulu. genus. J. Insect Physiol. 31: 593-601. Craddock, E. M., and W. E. Johnson Bristowe, W. S. 1979. Genetic variation in Hawaiian Dro- 1924. Notes on the habits of insects and spi- sophila. V. Chromosomal and allozym- ders in Brazil. Trans. Entomol. Soc. ic diversity in Drosophila silvestris and London 1924: 475-504. its homosequential species. Evolution Burkhardt, D., and I. De la Motte 33: 137-155. 1983. How stalk-eyed flies eye stalk-eyed flies: Cu6not, L. observations and measurements of the 1936. L'Espece. Paris: Doin. eyes of Cyrtodiopsis whitei (Diopsidae, Deschamps, M. Diptera). J. Comp. Physiol. 151: 407- 1957. Recherches morphologiques et biolo- 421. giques sur les Diopsidae du Nord-Cam- 1985. Selective pressures, variability, and sex- eroun. Bull. Sci. Min. Col. France Mer ual dimorphism in stalk-eyed flies Sect. tech. Agr. trop. 1-154. (Diopsidae). Naturwissenschaften 72: Eggers, F. 204-206. 1915. Diopsiden aus Deutsch-Ostafrika. Zool. 1987. Physiological, behavioural, and mor- Jahrb. Abteil. Syst. Oekol. Geogr. Tiere phometric data elucidate the evolutive 49: 469-500. significance ofstalked eyes in Diopsidae Emlen, S. T., and L. W. Oring (Diptera). Entomol. Gen. 12: 221-233. 1977. Ecology, sexual selection, and the evo- 1989. Big"antlers" are favoured: femalechoice lution of mating systems. Science 197: in stalk-eyed flies (Diptera, Insecta), field 215-223. collected harems and laboratory exper- Farmer, J. L. iments. J. Comp. Physiol. (A) 162: in 1984. Expression of ey in D. pseudoobscura. press. Dros. Inf. Serv. 60: 105. Burla, H. Feijen, H. R. 1954. Study on the polymorphism in Zygoth- 1984. Studies on the systematics, ecology and rica dispar and Z. prodispar, and de- economic importance of the Diopsioi- scription of Z. laticeps sp.n. (Drosoph- nea. Ph.D. diss., University of Leiden. ilidae, Diptera). Arq. Mus. Paranaense Frey, R. 10: 231-252. 1928. Philippinische Dipteren. V. Fam. Diop- 1955. Neue Ergebnisse zum allometrischen sidae. Not. Entomol. 8: 69-77. 24 AMERICAN MUSEUM NOVITATES NO. 2939

Grimaldi, D. reproductive competition in insects, pp. 1986a. The Chymomyza aldrichii species-group 221-230. New York: Academic Press. (Diptera: Drosophilidae): relationships, McAlpine, J. F. new neotropical species, and the evo- 1981. Morphology and terminology-adults, In lution ofsome sexual traits. J. New York J. F. McAlpine et al. (eds.), Manual of Entomol. Soc. 94: 342-371. Nearctic Diptera, vol. 1, chap. 2. Res. 1986b. A new Drosophila (Hirtodrosophila) Branch Agric. Can. Monogr. 27: 1-674. from Malaysia with broad-headed males McKinney, M. L. (Diptera: Drosophilidae). J. New York 1988. Classifying heterochrony: allometry, Entomol. Soc. 94: 372-376. size, and time. In M. L. McKinney (ed.), 1987a. Amber fossil Drosophilidae (Diptera), Heterochrony in evolution, a multidis- with particular reference to the Hispa- ciplinary approach, pp. 17-34. New niolan taxa. Am. Mus. Novitates 2880: York: Plenum. 23 pp. De la Motte, I., and D. Burkhardt 1987b. Phylogenetics and taxonomy ofZygoth- 1983. Portrait of an Asian stalk-eyed fly. Na- rica (Diptera: Drosophilidae). Bull. Am. turwissenschaften 70: 451-461. Mus. Nat. Hist. 186: 103-268. Nijout, H. F. 1988. Drosophila (Hirtodrosophila) chandleri 1986. Pattern and pattern diversity on lepi- (Diptera: Drosophilidae), a new species dopteran wings. Bioscience 36: 527-533. from Sri Lanka with broad-headed Okada, T. males. J. New York Entomol. Soc. 96: 1965. Drosophilidae of the Okinawa Islands. 323-326. Kontyiu 33: 327-350. Hunt, J. A., and H. L. Carson 1985. The genus Lissocephala Malloch and an 1983. Evolutionary relationships of four allied new genus of Southeast Asia and species ofHawaiian Drosophila as mea- New Guinea (Diptera, Drosophilidae). sured by DNA reassociation. Genetics Kontyui 53: 335-345. 104: 353-364. Oldroyd, H. Hunt, J. A., J. G. Bishop III, and H. L. Carson 1964. The natural history of flies. New York: 1984. Chromosomal mapping ofa middle-re- W. W. Norton. petitive DNA sequence in a cluster of Ouweneel, W. J. five species of Hawaiian Drosophila. 1970. Normal and abnormal determination in Proc. Natl. Acad. Sci. 81: 7146-7150. the imaginal discs of Drosophila, with Jaenike, J. special reference to the eye discs. Acta 1985. Parasite pressure and the evolution of Embryol. Exp. 1970: 95-119. amanitin tolerance in Drosophila. Evo- lution 39: 1295-1301. Ransom, R. Kaneshiro, K. Y. 1982. Eye and head development. In R. Ran- 1976. A revision of generic concepts in the som (ed.), A handbook of Drosophila biosystematics of Hawaiian Drosophi- development, 123-152. Oxford: Elsev- lidae. Proc. Hawaiian Entomol. Soc. 22: ier. 255-278. Sene, F. M., and H. L. Carson Land, M. F., and H. Eckert 1977. Genetic variation in Hawaiian Dro- 1985. Maps of the acute zones of fly eyes. J. sophila IV. Allozymic similarity be- Comp. Physiol. (A) 156: 525-538. tween D. silvestris and D. heteroneura Lande, R. from the island of Hawaii. Genetics 86: 1985. Genetic and evolutionary aspects of al- 187-198. lometry. In W. L. Jungers (ed.), Size and Shillito, J. F. scaling in primate biology, pp. 21-32. 1971. Dimorphism in flies with stalked eyes. New York: Plenum. Zool. J. Linn. Soc. 50: 297-305. Lindsley, D. L., and E. H. Grell Snyder, A. W. 1968. Genetic variations of Drosophila mel- 1979. Physics of vision in compound eyes. In anogaster. Carnegie Inst. Washington A. Autrum (ed.), Comparative physi- Publ. 627: 1-471. ology and evolution of vision in inver- McAlpine, D. K. tebrates, A. Invertebrate photorecep- 1979. Agonistic behavior in Achias australis tors, pp. 225-313. New York: Springer- (Diptera, Platystomatidae) and the sig- Verlag. nificance ofeyestalks. In D. Otte and R. Spieth, H. T. D. Alexander (eds.), Sexual selection and 1952. Mating behavior within the genus Dro- 1989 GRIMALDI AND FENSTER: BROAD-HEADED DROSOPHILIDAE 25

sophila (Diptera). Bull. Am. Mus. Nat. and Malaya. J. New York Entomol. Soc. Hist. 99: 399-474. 94: 226-234. 1981. Drosophila heteroneura and Drosophila Sturtevant, A. H. silvestris: head shapes, behavior and 1921. The North American species of Dro- evolution. Evolution 35: 921-930. sophila. Carnegie Inst. Washington Publ. 1982. Behavioral biology and evolution ofthe 301: 1-150. Hawaiian picture-winged species group Templeton, A. R. of Drosophila. Evol. Biol. 14: 351-437. 1977. Analysis of head shape differences be- 1984. Courtship behaviors of the Hawaiian tween two interfertile species of Hawai- picture-winged Drosophila. Univ. Cal- ian Drosophila. Evolution 31: 630-641. if. Publ. Entomol. 103: 1-92. Yoshimoto, C. M., and G. A. P. Gibson Stonedahl, G. M. 1979. A new genus of Eurytomidae (Chalci- 1986. Stylopomiris, a new genus and three doidea: Eurytomidae, Aximinae) from species of Eccritotarsini (Heteroptera: Brazil. Can. Entomol. 111: 421-424. Miridae: Bryocorinae) from Viet Nam

Recent issues of the Novitates may be purchased from the Museum. Lists of back issues of the Novitates, Bulletin, and Anthropological Papers published during the last five years are available free of charge. Address orders to: American Museum of Natural History Library, Department D, Central Park West at 79th St., New York, N.Y. 10024.

THIS PUBLICATION IS PRINTED ON ACID-FREE PAPER.