84 85 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 75 1976 ISOLATING MECHANISMS IN GOODEID FISH Ktumholz, L. A., J. R. Charles, and W. L. Minckley. Power, 13. M. 1970. Geographic variation of red. of these features among cyprinodontiform fishes, 1962. The fish population of the Ohio River. winged blackbilds in Cential North America. Carl Hubbs, working with Turner, used goodeid Pp. 49-89, 143-152, 165-180, 200-210. in: Univ. Kan .Mus. Natur. Hist., 19:1-83. Aquatic.life Resources of the Ohio River. Ohio trophotaeniae and ovarian anatomy in an exhaus- tive family classification (Hubbs and Turner, River Valley Water Sanit. Comm., Cincinnati, Seymour Ohio, 218 pp. . Effects of temperature upon 1939). Although a number of taxonomic papers on of vertebrae and fin rays in young including goodeids (deBuen, 1941, 1942; Turner, salmon. Trans. Amer. Fish. Soc., 88: Lindsey. C. C. 1954. Temperature-contmlled me- 69. 1946; Alvarez and Navarro, 1957; Alvarez, 1959, ristic variation in the paradise fish Marino() 1963; Alvarez and Cortes, 1962; and Romero, opercularis (L.). Canadian J. Zool., 32:87- have appeared since the Hubbs and Turner Snedecor, G. W., and W. G. Cochran. 1967. Statis- 1967) tical methods. Iowa St. Univ. Press, Ames, Iowa, revision, only one (Miller and Fitzsimons, 1971) Lindsey, C. C., and R. W. Harrington, Jr. 1972. 593 pp. significantly altered their classificatory scheme. Extreme vertebral variation induced by !Alper- Greatly influenced by Guillermo Mendoza's study attire in a homozygous clone of the self-fertilizing Vining, A. V. 1952. Experimental study of meristic (1965) with Xenotoca eiseni, Robert Miller and cyprinodontid fish !Grail's mormoratus. Cana- I judged trophotaenial and ovarian anatomy of dian J. Zool., characters in fishes. Biol. Rev., Cambridge 50(6):733-744, Philos. Soc., 27:169-193. goodeids likely too variable within a species to justify broader use in a family classification. MacCrimmon, R., and W. H. Kwain. 1969. Uyeno, T., and R. R. Miller. 1962. Relationships Through synonymies, we reduced the Hubbs- Influence of light on early development and of Empeirichihys erdisi, meristic a Pliocene cyprinodontid Turner classification by four genera and one characters in the rainbow trout, Salina fish from California. with remarks on the but in the same report managed to erect a eahdneri Richardson. Canadian J. species Zool., 47: Fundulinae and Cyprinodontinae. Copeia, 1962: new genus and species of uncertain phylogenetic (,3I-637. 520-532. affinity. Mlrir E. 1963. Animal species and evolution. During a revision of the goodeid genera (Fitzsimons, 1972), I Harvard Univ. Press, Cambridge, Mass., 797 pp. Accepted for publication May I, 1976. Characodon and Xenotoca learned that goodeids exhibit elaborate pair- forming rituals during courtship. Ethological Figure I. Males (above) and females (below) of data confirmed taxonomic interpretations of Xenotoca variata (A) 41.5 and 45 mm SL, X. eiseni X. melanosonta (C) 66.5 and 76. i v morphological information and, in many instances, (B) 33 and 38.5, and were better indices to relationships because atten- ETHOLOGICAL ISOLATING MECHANISMS IN GOODEID FISHES OF THE GENUS tion was drawn to features that the animals them- several localities along the Rios XENOTOCA (CYPRINODONTIFORMES, OSTEICHTHYES) selves used in distinguishing species. Although known from the study revealed certain elements of courtship to Tamazula and Tuxpan in southern Jalisco but be generically and specifically invariable, intra- has never been collected in the central Jalisco JOIN MICIIAEL FITZSIMONS' specific differences in two species of Xenotoca basins of the Rio Armeria or Rio Ameca which were unmistakable. This report examines these lie between its northwestern and southeastern Ansrancr: Although no natural hybrids are known, fertile laboratory hybrids were readily differences. limits. Xenotoca melanosoma is known only from obtained from Xenowa eiseni and X. inelanosoina in forced crosses in which a conspecific mate The genus Xenotoca includes X. variata (Bean), Jalisco. Near its southern limit, the type locality was not available. In choice crosses with males and females of both species, sympatric stocks X. eiseni (Rutter), and X. melanosoma Fitz- is in the Rio Tamazula about 16 km south by never hybridized, but allopatric fishes frequently mismated. Ethological data reveal differences simons (Fig. 1). Xenotoca variata, the type species highway from the town of the same name. It in courtship behavior and discriminatory ability in sympatric fishes not observed for allopatric , of the genus and perhaps the most widely distrib- ranges north into streams and ponds about 32 km conspecific stocks nor in fish from two populations of the congener X. variala. These uted goodeid, occurs in a variety of lentic and south of Guadalajara, east to Lago de Chapala, differences, which prevent interbreeding, are offered as evidence for the perfection of premating and west into basins of the Rio Ameca and Rio isolating mechanisms lotic habitats associated with the drainage basins in sympatry. Hybrid inferiority, essential for divergence in sympatry, of the Rios Verde and Aguascalientes in the state Grande de Santiago. Xenotoca eiseni and X. was reflected in reduced survival and inability to compete for males. of Aguascalientes, the Rio Santa Maria of San melanosonta have been collected together at sev- Luis Potosi, the Rio Grande de Santiago of Jalisco eral localities in the Rios Grande de Santiago and the Rio Lerma of Guanajuato, Tamazula. No natural hybrids are known, but in and Michoacan, . la Laja of Queretaro. Members of laboratory crosses fertile F ' hybrids have been The Gooch:id:lc is a family of about and the Rio de 35 species of hausted early in embryogeny and the young receive this species have not been taken sympatrically with produced from all combinations of allopatric and cyprinodontifortn freshwater fishes restricted to nutrition from the female through anal rosette either X. eiseni or X. melanosoma. Forced hybrid sympatric stocks when conspecific mates were the Mesa Central of Mexico. Goodeids differ or ribbon-like structures analogous to the placentae crosses (only heterospecific mates available) and riot available (Fitzsimons, 1972, 1974). In from their livehearing relatives, the anablepids, of mammals. These structures, called tropho- X. variata with its con- choice crosses consisting of males and females of jcnynsiids, and pocciliids, in having true viviparity artificial inseminations of tacniae, were studied in detail by thc embryologist geners have been unsuccessful. The distribution of both species, members of allopatric stocks some- rather than ovoviviparity in which embryos de- Turner (1933, 1937). Realizing the uniqueness X. eiseni is disjunct. In Nayarit, it occurs in the times hybridized but sympatric fishes never mis- velop at the expense of yolk in retained eggs and Rio Compostela and above 600 m in the drainage mated. receive little or no nourishment from the mother. basin of the Rio Grande de Santiago in which it The maintenance of X. eiseni and X. melano- In all Mus. Zoology and Dept. Zoology and Physiology, but one goodeid species, the yolk is ex- Louisiana State Univ., Baton Rouge, Louisiana 70893. ranges into northwestern Jalisco. The species is soma as discrete species depends on the presence 4

87 86 BULLETIN SOUTHERN CALIF° RNIA ACADEMY OF SCIENCES VOLUME 75 1976 ISOLATING MECHANISMS IN GOODEID FISH EL of one or more premating isolating mechanisms aunt species-specificity, the displays of courting RIO SANTA PRESA which prevent their interbreeding. For sympatric males showed a greater promise for use in taxon- GIGANTE populations of these species there are two possibil- omy (Fitzsimons, 1972; Fitzsimons and Le- MARIA ities ( Mayr, 1965): either potential mates do not (irande, 1974) and in the study of ethological meet (seasonal or habitat isolation) or potential isolating mechanisms. The displays are assumed mates meet but do not mate (ethological isola- to be inherited and relatively unmodified by ex- tion). There is no evidence for seasonal or habitat perience rather than learned characteristics because HEAD- isolation. Females of the two species bear young they were identical in animals with conspecific FLICKING 1 '5' throughout the year when kept in aquaria, and experience only, heterospecific experience only, '9 29 2 36 pregnant females and neonates of both species are and in those with no experience at all, i.e., ones 29 9 29 found in collections made during the same times raised in complete isolation. For at least two of the year from sympatric and allopatric popula- goodeid species underwater observations in Me- LATERAL T - tions. Their ecological requirements are similar xico indicated that reproductive behavior in F ORMATION (Fitzsimons, 1972), and there is no apparent dis- aquaria is the same as that which occurs naturally continuity in their distribution at a given locality— (Fitzsimons, 1972). both species can be caught in the same seine haul. 23 17 25 14 Thus, differences in mating behavior are likely alone responsible for preserving the integrity of METHODS these two potentially hybridizable species where L ATERAL they are sympairic. This paper examines the Materials and methods included certain of those TILTING nature of ethological isolating mechanisms opera- used in a recent revision of Xenotoca (Fitzsimons, tive in Xenotoca variata, X. eiseni, and X. melano- 1972). Live stocks for behavioral studies and 9 7 9 ('? 3 soma and, for the latter two species, suggests how hybridization experiments included X. variata: these mechanisms have evolved toward greater Rio Santa Maria, ca. 1.6 km S Villa de Reyes, San efficiency in sympatry. Luis Potosi, R. R. Miller and H. L. Huddle, III: 26:1968; Presa El Gigante, near Santa Maria de Gallardo, 21 km NE (Hwy 45) on road to Loreto ROUND GOODEI D COURTSHIP (at La Dichosa), Aguascalientes, R. R. Miller, H. DANCE L. Huddle, and J. Gomez, IV: 1:1968; X. eiseni: Internal fertilization and viviparity require that Manantial El Sacristan, 1.3 km NW plaza Topic, there be sexual selection and pair-forming for suc- Nayarit, C. M. Bogert, 1955; X. metanosoma: 15 13 cessful reproduction. In goodeids the male initiates Presa de la Vega, in Rio Ameca, 32 km W jct. is pair-forming activities by orienting toward the Hwy 15 and Hwy 70 (to Ameca), Jalisco, R. R. female, approaching her, and performing one or Miller and H. L. Huddle, V:5:1966; and X. eiseni more courtship displays. Male courtship displays and X. Inelanosonta: Rio Tamazula (at Hwy 110 HALF-DANCE range from simple broadside presentations to the bridge) 5 km S Cd. Guzman turnoff, Jalisco, R. R. female to intricate dances in which the male Miller and H. L. Huddle, V:3:1966. maximizes the exposure of sexually dimorphic Fishes were maintained in the large aquarium ' features, particularly color and elongate fins. facility directed by Robert R. Miller at the Univ. 11 r 2 Female courtship behavior is much simpler. If Michigan Mus. Zoology and in my laboratory at the female is receptive to the male, she will respond Louisiana State Univ. by Head-Wagging, a rapid side-to-side swinging of Courtship observations and discrimination tests LATERAL the head and anterior body. Similar movements were conducted in a IS or 20 gallon aquarium have been reported for other cyprinodontiform masked on three sides with black paper. The open WHEELING fishes by Foster (1967). In goodcids Head- side of the tank faced a black sheet with a one-way 8 7 Wagging is usually restricted to sexually receptive mirror mounted at its center. The mirror was behavior by the female and rarely is incorporated tilted so that only the darkened ceiling of the into male courtship displays. In observations of room was reflected toward the aquarium. An OBLIQUE 21 species of goodeids, the courtship movements overhead fluorescent fixture illuminated the tank, of females were very similar and consisted of and the room was darkened. About 240 hours of stereotyped receptive behavior (Head-Wagging) courtship observations were tape-recorded. A 5 7 2 or rejection behavior (Evading. Hiding, Attacking, minimum of 20 males and 20 females of each Xenotoca variata. (The Figure 2. Male courtship display complement in two populations of Pseudo-Feeding. and others). Interspecific dif- population was studied; half the pairs were indi- number to the left of each display indicates its percent frequency of occurrence in the total ferences in courtship were much more marked in viduals raised in complete isolation. Fourteen display complement; the number to the right is the percent effectiveness of the display in males. Because of their complexity, variability, pairs of laboratory hybrids were available for mate achieving successful copulation.)

' 89 88 BULLETIN SOUTIIERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 75 ISOLATING MECIIANISMS IN GOODEID FISH selection experiments. In discrimination tests the in Head-Wagging. Head-Flicking consisted of a MANANTIAL EL RIO TAMAZULA aquarium was divided into three equal parts by single lateral movement, a burst of three or four SACRISTAN opaque plastic partitions. The fish to he tested at a time, or a continuous series up to six seconds was placed in the center compartment and the duration. The male Head-Flicked while stationary "choice" fishes in the outer two. After fishes in front of and broadside to the female, oblique acclimated to new surroundings, partitions were and head-on, lateral and parallel, or while swim- removed and observations begun immediately. If ming actively in any of these positions. DANE E a test male displayed to the female of his own In the Lateral T-formation display, a male ap- species, a conspecific point was scored. If he proached a stationary female from her right or displayed to the female of the other species, a left, stopped broadside about one body length or 35 9'9 16 heterospecific point was scored. Test points for less in front of her, and spread his median fins. females were based on their Head-Wagging re- The body was held straight and the caudal fin sponse to male displays. To preclude the possi- was flicked or jerked conspicuously. bility that a male might select the conspecific In another type of lateral display, extreme tilt- HALF-DANCE female because the heierospecific choice was, for ing and S-curving were seen. In this Lateral any number of reasons, not in equivalent repro- Tilting display, the male also quivered his body, ductive condition, males of each species (and causing the fins, particularly the dorsal and anal, population) were tested consecutively against the to flutter markedly. same set of choice females. If one of the females In the Round Dance, a male briefly assumed was inferior, it became evident by watching her the posture seen in the Lateral Tilting display, LATERAL T- behavior in the presence of a conspecific male; quickly circled in front of the female, and again F ORM AT I ON when necessary, tests were repeated with another resumed the lateral presentation with strong S. female in good reproductive condition. A parallel curving, tilting, quivering, and with the anal fin procedure was used in testing the discriminatory inclined toward the female. Circling was often 7 ability of females. A closed sequential test grid repeated several times (two to six, usually three) 281 (('ole, 1962) was used to determine the number but each circuit was separated by the stationary L ATERAL of animals and the number of tests per animal posture held briefly before the female. required to indicate differences of predetermined In the Half-Dance display, a male postured as in WHEELING statistical significance ( P = 0.9 for discrimination the Lateral Tilting or Round Dance, immediately and P = 0.5 for nondiscrimination). Test animals swans a half circle, and again postured. If the 13 4 13 \( 0 included individuals of varying experience (exclu- female was receptive (Head-Wagged), the male sively conspecific, exclusively hcterospecific, or usually continued into the Round Dance. heads no experience). A male performed the Lateral Wheeling display OBLIQUE cLo.w.p, in response to an actively swimming female. He swam forward from the rear of the female, arced COURTSHIP MOVEMENTS around in front of her from the right or left, 9 0 braked with expanded pectorals, tilted, S-curved, Qualitative features of courtship displays of Figure 3. Male courtship repertories in two populations of Xenotoca eiseni. (Numbers to the and quivered his body and fins as in the Lateral ..„ left of displays indicate percent frequency; numbers to the right are percent effectiveness in Xenotocn males were used for taxonomic purposes Tilting display. This display effectively blocked,.*': in the generic revision (Fitzsimons, 1972); the the path of the swimming female. achieving copulation.) descriptions below have been expanded to include Males performed the Oblique display by facing populational differences. away from the female on an oblique angle less than Xenoloca eiseni.—Males from the Rio Tamazula gression of the male approximated her swimming Xenotom with:Ia.—The courtship displays of X. one body length in front of her while tilting and exhibited five courtship displays; fish from Manan- speed so that the Dance appeared more like a vanilla males included Head-Flicking, Lateral T- S-curving; the caudal fin was brought close to her tial El Sacristan had four (Fig. 3). The Loop series of stretched-out loops than smooth figure- formation, Round Dance, Half-Dance, Lateral head. In this position the male quivered its body Dance, Half-Dance, Lateral T-formation, Lateral eights. At the end of each leg of the Dance, the Tilting, Lateral Wheeling, and Oblique (Fig. 2). rapidly causing the semi-erected median fins, Wheeling, and Oblique displays comprised the dis- male turned back to describe a loop before con- Head-Flicking was the most frequent display especially the dorsal and caudal, to flutter vio- play repertory of Rio Tamazula males; males from tinuing. During turning movements, the male presented to stationary or moving females; it was lently. Manantial El Sacristan did not perform the strongly inclined the dorsal and especially the anal Rio similar to or identical with the courtship display I was unable to detect individual or populational Oblique display. fins toward the female. When turning, a reported for males of many killifishes (Foster, variation in the form of courtship displays in The most elaborate display was the Loop Dance, Tamazula male exhibited exaggerated sigmoid 1967). The male rapidly twitched the anterior Xenotoca ;what: males from Rio Santa Maria in which the male executed a series (one to six, flexures and often tilted so much that the vertical end of his body in a manner reminiscent of female and Presa El Gigante; moreover, populational usually four) of figure-eight movements slightly plane of his body became nearly horizontal. A receptive behavior (Head-Wagging), but the arc differences in the frequency of individual displays above (about half a body length) and one to two male from Manantial El Sacristan lacked sigmoid posturing throughout the display and, when turn- described by the right and left lateral movements and their effectiveness in achieving copulation A body lengths ahead of a swimming female. If the ing, the fish tilted only rarely and very slightly was much smaller and more quickly executed than are surprisingly small (P = 0.01; Fig. 2). female was swimming rapidly, the forward pro-

90 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 75 076 ISOLATING MECHANISMS IN GOODEID FISH 9! PRESA DE LA RIO TAMAZULA (never more than 15° from the vertical). A Rio Tamazula lacked sigmoid posturing; Tilting was VEGA Tamazula male quivered violently when the path rare and never exceeded 10°. , of the display brought him close to the female; a The Zig-zag Dance of the Press de la Vega male on male from Manantial El Sacristan never quivered. consisted of a series (two to six, usually three) of c4-04e The Half-Dance display consisted of the male to-and-fro movements during which the male DANCE swimming the first leg of the Dance, but, rather swam one to two body lengths in front of, and at than continuing to complete a figure-eight, he the same swimming depth, as the female. As the stopped short in the second run. In the halted male went through each turn, S-curving was c d b v position only the male from the Rio Tamazula extreme; in the transverse portion of the Dance, rI2 12 c' 3 tilted and quivered rapidly. This display was quivering and inclination of the dorsal and anal presented to a stationary or slowly swimming fins toward the female were marked. Restricted to the transverse legs of the dance, tilting was infre- I , female. HALF-DANCE CO" . The simplest display was the Lateral T-formation quent and never exceeded an angle of 10°. The where the male swam across in front of the female, amplitude of the lateral movements was one to two braked with expanded pectoral fins, assumed a body lengths, and the pattern traced as the male (1? slight sigmoid shape (Rio Tamazula fish) or held moved forward appeared as a series of meanders 14 4 0 the body straight (Manantial El Sacristan fish), if the female was actively swimming forward or LATERAL head toward and caudal fin away from the female, it was compressed into sharper cornered zig-zag T- on dorsal and mainly anal fins conspicuously bent movements if the female was stationary or swim- F ORMATION toward her, and the dorsum of the body tilted ming very slowly. In the shortened Zig-zag Dance * toward her (Rio Tamazula fish). The male from of Rio Tamazula fish, the male swam slowly across 29' 20 5 the Rio Tamazula also often quivered slightly. from the right or left in front of the female, cP'7 10 This display was presented to a stationary or very turned back to complete a second leg, stopped, L ATERAL slowly swimming female. and spread his median fins as in the Lateral T- If the female was actively swimming forward, formation display. The Dance rarely extended WHEELING the male approached from the rear, tilted (Rio to the beginning of a third leg. The Dance was Tamazula fish), wheeled around in front of her presented to stationary or very slowly swimming from the right or left, stopped, and assumed the females. 3 I I 6 posture seen in the Lateral T-formation. This is In the Half-Dance display, the male from Press the Lateral Wheeling display. de la Vega swam the first leg of the Dance, stopped OBLIQUE • In the Oblique display, seen only in Rio abruptly in the second leg, and assumed a pro- Tamazula fish, the male faced the female from an nounced sigmoid posture while quivering and tilt- angle less than 90° on her right or left, assumed ing (dorsum away from the female) with the a head-down posture with the body at an ap- dorsal and particularly the anal fins erected and 7 3 proximate 45° angle to the horizontal, and bent bent toward the female. If the female was respon- HEAD the caudal fin and peduncle toward her. The sive, the male usually continued into the dance. In ...Ak) dorsal and anal fins were strongly inclined toward the Half-Dance display of Rio Taf szula fish, the WAGGING the female. This display was presented only to a male approached from the rear 1r side of a pationary female. stationary female, quickly swam in front of her, 27 9 Populational variation in the form of male braked with pectoral fins, and backed slowly with courtship activities was conspicuous in Xenotoca his dorsal and anal fins fully expanded. If the eiseni from the Rio Tamazula and Manantial El female was not receptive, the male held the Sacristan. Statistically significant interpopulational backed position for several (one to five) seconds, DART differences were seen in the frequency of indi- conspicuously twitching his dorsal and caudal fins vidual displays and in the relative effectiveness of before repeating the forward movement of the these displays in gaining copulation. These dis- display. If the female was responsive, the male 12 3 crepancies are interpreted below with those de- usually repeated the forward darting movement L scribed for the populations of X. melanosoma. and,continued into the short Zig-zag Dance. ATERAL Xenotoca melanosoma.—Males from Press de la In the Lateral T-formation display, a male ap- SIDLING Vega exhibited six courtship displays (Fig. 4): the proached the female from her right or left and Zig-zag Dance, Half-Dance, Lateral T-formation, paused while broadside in front of her. The male ,Lateral Wheeling, Oblique, and Head-Wagging. from Presa de la Vega quivered rapidly in the 2 In addition to these, Rio Tamazula males showed display, bent his body into a strong sigmoid pos- Figure 4. 1 Elements of male courtship in two populations of Xenoloca inelanosonia. (Numbers the Lateral Sidling and Dart displays. ture, with the head toward and tail away from to the left of displays indicate percent frequency; numbers to the right are percent effectiveness The male courtship displays of fish from the Rio the female, and tilted, dorsum away from her. The in achieving copulation.) 92 BULLETIN SOUTIIERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 75 1976 ISOLATING MECHANISMS IN GOODEID FISH 93 TABLE I. Dance and Half-Dance displays in Xenotoca males. TABLE 2. Lateral T-formation and Wheeling displays in Xenotoca males. X. rarlata X. variata Rio Santa X. theta X. roriata X. rascal Presa El X. risen! Manantial X. ,,leIanoxon,g metanosoma X. varied° tortanotoona Maria Gigante Rio X. Rio Santa Pre. El X. Meal Manantial X. melanotonta X. Tamarala El Sacristan Rio Tamazuta Presa de to Vega Maria Gigante Rio Tammula El Sacristan Rio Tamazula Presa de la Vega Path described circles circles figure- figure- zig-zags none strong by Dance zig-zags S-Curving none (Lat T) none (Lat T) slight none eights or eights or to strong to strong loops loops (Wheeling) (Wheeling) Path described half-circle half-circle one loop one loop forward and half zig-zag by Half-Dance Tilting backward extent none (Lat T) none (Lat T) moderate none or none moderate straight line to extreme to extreme very to extreme movement (Wheeling) (Wheeling) slight Number of circles, 3(2-6) 3(2-6) 4(1-6) 3(1-6) 2 or, rarely, 3 venter loops, or 3(2-6) direction dorsum dorsum dorsum dorsum zig-zags toward toward in Dance toward toward toward female female female female female S-Curving strong strong none or none none strong uivering none (Lot T) none (Lat T) slight slight none strong slight to strong to strong Tilling ( Wheeling) (Wheeling) extent moderate moderate extreme none or none very slight dorsal, anal dorsal, dorsal, dorsal, caudal dorsal, anal to extreme to extreme Fin movements dorsal, anal very (Dance) to spread; spread; anal anal expanded; inclined slight extreme (Half- caudal caudal inclined inclined anal slightly toward Dance) flicked flicked toward toward inclined female female female toward (lit ection dorsum dorsum dorsum dorsum venter (Lat T) or (Lat T) or 1 female toward toward toward toward toward fluttered fluttered female female female female female Quivering strong strong strong none none strong trs striking to-and-fro or see-saw-like movement was Fin movements fin. The dorsal fin was alternately raised and dorsal, dorsal, median fins median fins median fins median fins lowered (Rio Tamazula males) or only slightly produced. The Dart display was presented to caudal caudal expanded; expanded; spread but expanded; expanded so that the movements of the body stationary females. expanded; expanded; dorsal, dorsal, not inclined dorsal, anal In the Lateral Sidling display of Rio Tamazula anal inclined anal inclined caused it to flutter conspicuously (males from anal inclined anal inclined toward inclined fish, the male moved alongside the stationary or toward toward toward both populations). The anal fin was inclined toward female; toward slowly swimming female with his dorsal fin in- female female female female dorsal and female toward the female. Except for median fin move- caudal also ments, this display resembled receptive behavior clined so that it brushed, or nearly so, the back twitched in in the female and, accordingly, is called the Head- and head of the female and, once past her, he Half-Dance Wagging display. It was presented only to sta- turned in and assumed the posture seen in the other tionary females. lateral displays. In comparison to the courtship behavior ob- 0 A male from the Rio Tamazula stock sometimes semi-erected dorsal and anal fins were strongly at an angle less than 90 to the right or left in approached the female from the front or rear, right served for the two populations of Xenotoca variata inclined toward her. A Rio Tamazula male held front of a female. In Presa de la Vega fish,- the or left, and performed the Dart display in which (Fig. 2), there are noteworthy interpopulational its body straight, the dorsal fin erect, and the anal male faced away from the female and held his quickly sprang across in front of the female differences between X. eiseni from the Rio Tama- Ito he straight ( usually) or slightly inclined toward body in a strong sigmoid flexure, head toward and with the dorsal and anal fins lowered, stopped sud- zula and Manantial El Sacristan and between X. the female. The lateral T-formation display was tail away from the female, while quivering rapidly denly with expanded pectorals, and sculled back- melanosoma from the Rio Tamazula and Presa de presented to stationary or slowly swimming fe- with the dorsal and especially the anal fins inclined ward while erecting the dorsal fin and inclining the la Vega (Figs. 3 and 4). In my opinion these dif- males. toward her. The Rio Tamazula male held his body anal fin toward her. The forward movement of the ferences are attributable to the reinforcement of In the Lateral Wheeling display, the male ap- at an oblique angle to the female and presented Dart ceased when the trailing edge of the dorsal premating isolating mechanisms where the two proached the swimming female front the rear, his right or left side and median fins fully ex- fin was directly in front of the female, and backing species are sympatric. wheeled around in front of her, and assumed the panded but not inclined. stopped when the leading edge of the fin was about The most striking difference between the court- stationary posture described for the Lateral T- A male from either population sometimes ap- in the same position. The Dart display consisted of ship repertories of the two populations of X. eiseni formation. At Presa de la Vega, tilting occurred 0 proached a female from the side or front, turned two to six such forward and backward movements is that the Loop Dance was the only display which throughout the male's display; it was slightest (10 broadside to her, and rapidly bent his body into in rapid succession with the raising and lowering led directly to successful copulation in the Rio or 0less) during wheeling and greatest (up to about a series of horizontal C-shapes. Moving through of the dorsal fin its most conspicuous feature. Tamazula population, sympatric with X. melano- 25 ) during lateral presentation. The Lateral a greater arc than the rest of the body, the head Although similar to the Half-Dance in general pat- soma, but in Manantial El Sacristan fish, allopatric Wheeling display was presented to actively swim- was jerked erratically right and left while sculling . tern of movements, the Dart display had a much to X. melanosotna, displays other than the Loop ming females and, less often, to stationary ones. movements of the pectoral fins offset the pro- smaller amplitude and quicker repetition of the Dance led to successful copulation in nearly one- In the Oblique display, a male took up a position pulsive force of the flexing caudal peduncle and backward and forward components so that a third of the observations. Readily distinguishing

'