(Osteichthyes: Teleostei:Ofperciformes) from Lake Tanganyika

JapaneseJapaneseSociety Society ofSystematicZoologyof Systematic Zoology

Species Diversity,2003, 8, 1-26

Comparative Osteology the Infraorbitals in Cichlid Fishes

(Osteichthyes: Teleostei:ofPerciformes) from Lake Tanganyika

Tetsumi Takahashi

Jtipan Science and Technology Cbr:poration, Dornestic Research Eellow. Lake Biwa ltttltseum,

Shiga Prnjlecture, Oroshimo ICZ91, Kttsatsu, 525-OOOI tlapan E-mail: [email protected]

(Received 14 May 2001; Accepted 15 November 2002)

The inhaorbitals of representatives of all Lake Tanganyikan cichlid genera were examined in order to establish a basic morphological data base. About half of the genera examined displayed imbaorbitals of type A, the most plesiomorphic arrangement among Aflrican cichlids. The remaining taxa were divided among seven types of infiraorbital patterri. Types B and C were fbund in all examined members of the tribes Ectodini and Tremato- carini, respectively, and thus appear to be synapomorphies supporting each tribe's monophyly. Type D was found in all of the species of Lamprologini examined except IVeolamprologus toae (Poll, 1949), whieh has the type E condition as an autapomorphy, and Vtiriabilichromis moorii (Boulenger, 1898>, which appears to have retained the primitive type A, indicating that this species is better placed in a basal position in the tribe, The phylogenetic im- plications of types F, G, and H remain unresolved, Key Words: Cichlidae, Lake Tanganyika, infiraorbital, osteology, tribe,

Introduction

"ancient The three great lakes" (sensu Gorthner 1994) in the East African Rift Valley (lakes Victoria, Tanganyika, and Malawi) each harbor hundreds of species of the family Cichlidae, almost al1 being endemic to their particular lake (Green- wood 1991). These fishes are characterized by great morphological, ecological, and behavioral diversification (Fryer and lles 1972). On the basis of recent molecular analyses, the cichlid fishes in Lake Tanganyika, the oldest of the African ancient lakes (estimated at 9-20 million years) (Tiercelin and Mondeguer 1991; Cohen et al. 1993), are believed to be a polyphyletic group (Nishida 1991, 1997; Takahashi et al. 1998), while each of the Victorian and Malawian assemblages is likely to have been derived from a single ancestrat lineage (Meyer et al. 1990; Kocher et al. 1995; Sultmann et al. 1995; Mayer et al, 1998). The morphologieal relationships of Tanganyikan cichlid fishes have been treated by several workers on the basis of a single character or a complex of a few characters, such as the pharyngeal apophysis and ethmovomerine region (Regan 1920), caudal skeleton (Vandewalle 1973), pharyngeal apophysis (Greenwood 1978), intestinal coiling pattern (Zihler 1982; Yamaoka 1985), and ethmovomerine region (Takahashi 2001). With regard to the infraorbitals, Stiassny (1991) indicated the plesiomorphic condition for African cichlids to be a single plate-like bone (IOI) with five marginal

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2 Tetsumi Takahashi

canals, fo11owed by five tube-like bones (I02-IO6, I06 being the dermosphenotic). For the Tanganyikan eichlids, Liem (1981) and Greenwood (1983) argued for a phylogeny of some ectodine taxa based on morphological investigations, including descriptions of the lachrymal (IOI), and Colombe and Allgayer (1985) and Stiassny (1997) also utilized infr'aorbital evidence in classifying taxa in the tribe Lampro- logini. Despite this, the morphology of the infraorbitals has stM not been studied

extensively in Tanganyikan cichlid fishes. Poll's (1986) classification of Tanganyikan cichlid fishes included the establish- ment of 12 tribes, supported by short descriptions of external morphology and ref erences to Greenwood's (1978) observations of the pharyngeal apophysis. These tribes have been in approximate agreement with the results of several molecular analyses (Nishida 1991, 1997; Kocher et al. 1995; Takahashi et al. 1998), although some contradictory points remain. Recently, emphasis on morphological studies of these fishes has decreased considerably, in contrast to the advance of molecular studies. This may be one of the main reasons why the taxonomy of Tanganyikan cichlids is stil1 in many respects problematic. It is important that emphasis on morphological analyses be continued, if taxonemic problems are to be convinc- ingly resolved. In the present study, the infraorbitals of representatives of all Tanganyikan cichlid genera have been examined in order to establish a morphological data base that lends itself to the reso}ution of taxonomic problems.

Materials and Methods

The inhaorbitals of 89 ctchlid species from Lake Tanganyika, representing 51 genera and 12 tribes, were examined (Table 1). Specimens were identified by comparison with the descriptions of Boulenger (1898, 1901), Trewavas (1953, 1983), Poll (1956, 1974, 1978, 1979, 1981, 1985), Marlier (1959), Poll and Matthes (1962), Poll and Stewart (1975), and Bailey and Stewart (1977). The infraorbitals were dissected, observed, and drawn under a Nikon SMZ-1000 or Leica MZ12 btnocular microscope. "infraorbitals" The fo11owing terms are used: (abbreviated to IO) are the bones usually bridging between the lateral ethmoid and sphenotic of the neurocranium, rim- ming the ventral half of the orbit, and counted from anteriormost to posteriormost (infraorbital number may not be homologous between inhaorbital types; for exam- "dermosphenotic" ple, I04 of type A is not homologous to I04 of type B); is the name applied to the posteriormost infraorbital, which is firmiy attached to the sphenotic.

Institutional codes are as follow: HUMZ, Laboratory of Marine Biodiversity,

Graduate School of Fisheries Sciences, Hokkaido University, Japan; LBM, Lake

Biwa Museum, Shiga Prefecture, Japan; MRAC, Musee Royal de 1'Afrique Cen- trale, Tervuren, Belgium; and UMMZ, University of Michigan Museum of Zoology, U.S.A.

Results

The infraorbital series comprises firom one to nine elements. The anteriormost

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’ Infraorbitals ot Tanganyikan cichlids 7

自 Q ∩ ρ ∩ AO OOoo A 国国国国国国 n ＜＜』「』国 ←

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○つ寸卜旨ハ鬥 OH o つ Oo ト目』 ⊇ ．．色ゆ一羇旨噂卜 σ◎ 一一〇 Q 】】 ρ ≧ ≧ 寸 ≧ ≧ H 一．卜 σ○ 霞国 qq ロココ 5 OQ q 舘円日ト囗一日日一例一自ゆ．ハ．．ハ．鮎 Φ 辞の寸 o ＝州一 O 卜 o つ〇寸 NQQo 爲 0 ゆ〇 D め〇目目一 o つ鴫露． OD つ霧雷 QO H 舘巨毫一＝トの N 一 OQoO 円卜聰〇つ Q ◎ 圉州の〇Do の切 Q ◎ 卜 N 卜崘ト Qoo 嶋卜円う N 〇謌爲 H m 羇［ eq oQ ごq o ううう黷一一霧【一 ◎ o 崘基頃一一一一一一躊一一目一一一目 HN 鬥一 HN2P鬥一制邸鑰国ゆ覊 8N 代い．霜 N N N N N 爲 N N NO N ド N 邸 N N N N N 】】】】】日】一】］ト遍〜 6 〉 ≧ ≧ 寸 Q ≧ 匿 ≧ 黜 H 芝 ≧ ≧ ≧ 自謡鴫芝芝芝芝【 ≧ ≧ 薯薯ロごhN hF h hP hP hP h h D P P oつ P P 国ロ卩釦自q 国凵 P P 二二口鳴甲崘靄日国日＝｛囗目口＝頃国ごq ＝＝口田山寓囗頃寓 H 国 H 寓 H

賦づ（ qD （ Q98 』弓 o 」 O （邑pOO の QD 目（僑祠゜⊃ ．守 ◎o 〉、（旨 φ の邸゜。 Qo Φ 一紹旨【窃 b め、鬥韓 Qo 一唱 ap ．口【（、』一口』』口＝ O 寸に Φ 軌一 Φ O 。。角ら卜 ← 〇一 ∀ 冒）湿ヨ口 Φ 、 O 一 O 口的 bD 鬥 Om 』 ○ 国．識（目邑ミ【）【軸ヨ ω 』 O 【）自目 O 唐 50m 寸韓 o うミ Φ ヨ bD β 、寒山識 H 品 O h 粕 ℃ 恥象 O 口） UO にロミ鵠謡）ミ、口 bD 粒一超一唱 9 【唱ヨミ O ごコ自口ぎ」爻ミ O 巷 O N O q9 山ミ爻 O 一 kq 旭ご）樋冨ミ」 QQ 国一口電ミ唱恥軸＆亀鳶謡のの Om 昌恥奄 O OON 」ミミ嵩寒窪鳥ミ Me 弐 Q む鳳ミミミ q ゆ」丶総 Q ぎの劬り Q 噛恥の離、稔遷量識譜遣嵩越遣寒跫自 Ok OkB b ミの kb 鴇刀 ◎ 軸劬軸ミ O 鳥 O ぎぎぎ O o 」 ◎ ミ NOk NO 丶ミ（ミ丶 ε 丶 ⇒ O O N Ok Ok Ok9 心のリ的 § ミゆ盞 9 一口」」」のミミ塁祠 O 認信一、謹嵐息鼻一亀風 8 OQ OQ OO qOO ゜・ O ミ．ミミミお冨 9 塙ミ §O ミ遠邸 28q 旭旭己 O 口むむ ◎ 壱熟 ◎っ丶 NO 、 ρ N 鴇ミミ、、 O 息き凝 O O O O O O § 忙ら軸穐 NO ． O 一山一融鈔融趣融融避二 O む紹のくくく自謹一 § § くくくく邸閃国鴫』【国 ρ ← 邸 ←

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o 翁＜ O o 〈 O ＜＜ ooooo ぐ＜卜

興 ζN 己N σ澗嗣じ電じ繭 NN ¢ 『

go 的 N 『ロ囚 N Nc （（罵匚つ CQ ← ∀ ）一 σQ ρ N N 』 O 頓鴫 u つ寸寸 u つ u つ c 刈 Ncu 邸と咽囚一寸一一一口鬥囚囚 o 個 ooo

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．帽 O 韓（ 9 σつのゆ（ c 南（ Oo HO （唱一つ（ OD o っの（誉 Φ （頴 H ロ 6 一 Oa HO 邸（頃 o っ． ON 一あ一〉 8 h 、づ一一（一帽 n 郎』一〉』． H ．一』 bD Qa ．罵邸 Φ 汐、 ◎ρ 口』（ O 口 8 O ゆ国 ⇔p 寸自一口』 dD 自〉）口一の O 山凱等臼口［邸【）一．り β b ゆ一 ⊆ 綜目一． PO と O 劬〇噂窒つ口嵩一 NO 帆冒自口一 O 合餡幅山 50 一ミ o ） O ）国）口Q り） O ミ〇鶚）の）山 O 芍 N 国山壇黛巴識雨む嚇階） O ）赴廴辷む畏め局勉． 9 謡踊ミ魯（む揖蝕 O 丶讐卜魯ミミ塁謎 O 総、偽 O 心ミ辷」爻 O 葛凡暑ゆ O 謎ミむミ O ε 栓一恥」 q 軸暑） N q 讐 O ℃ O 8 」 § O § ミ惚総惣 N ミあミ一総樋避飽雄穂 Ok ℃ d 総り一詮聡口 Φ ミミ建辷ミの偽眉 O ミミミ q 哉ミ O O O O o りコ Ok 」」鷙 o 」 O O § ミ 9 輔日」」肩邸ロミ赴 60 」 £ 」口 Ok Ok 瓮刺ミ O ミ QO ミ凝耳一』ミ QO 90 90 O の O 9 竃 9 り』母心 QD 口二（ミ 9 崎卜赴ミ建磐 6 稔暑 OQ 嚇 UO ミミ丶二訂卜 N 醤穐建 q 〇黛」 ◎ 日ぢ丶む軸輸ミ鴇 O O 肄摘一」 O ． Φ o 口雪舘』 O 勉匿ミ」一 ρ 竃黔袋と身ミ箱 O O O q 嘱葭歯自 U δ ξ Φ 眉鎖あ僑一日り一 ρ 卜〇 O 自臼脂

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Inhaorbitals of Tanganyikan cichlids 9

infraorbital (IOI) is a large, plate-like bone, dorsally articulating with the lateral ethmoid and bearing a sensory canal that branches into three to seven marginal canals and opens through a sensory pore located at the external end of each marginal canaL The other infraorbitals usually comprise a series of tube-like bones, forming a sensory canal located below and behind the eye. The sensory canal on each bone opens through at least two sensor'y pores located at the anterior and posterior ends of the bone. Additional sensory pores are occasionally present between these pores, the total number of pores on each element being expressed for descrip- tive purposes. The dermosphenotic is usually present. Tilapiini (Fig. IA, Table 1). Infraorbitals number six. IOI is a square or rounded bone with five sensory pores. I02-I06 are tube-like bones continuously arranged in a single series, with two sensory pores each. I02 ls short and anteriorly overlaps the posterior part of IOI. I03 is short, approximately the same length as I02 and anteriorly touching the latter. I04 is the most elongated of the five tube- like bones and anteriorly touches I03. I05 and I06 (dermosphenotic) are shorter than or the same length as I04, and each anteriorly touches the preceding bone.

This condition is named type A. Haplochromini (Fig. 2, Table 1). The infraorbitals of Ctenochromis horei fo1- low the type A pattern (Fig. 2A). In one specimen of Astatotilapia burtoni and three specimens of Ctenochromis benthicola, the infraorbitals were in accordance with type A. On the other hand, in

three specimens of A, burtoni and one specimen of C benthicola, there were oniy five, not six, infraorbitals, with three sensory pores on the elongated third inhaor-

- -

Fig. 1. Ilnfraorbitals. A, Tilopia rendalli, representing tribe Tilapiini; B, 11ylochromis

polylqpis, representing tribe Tylochromini.

- -

Fig. 2. Infiraorbitals of tribe Haplechromini. A, Ctenochrornis horei; B, C benthicola.

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Fig. 3. Infiraorbitals of tribe Tropheini, A, Petrochromis polyodon; B, Lobochilotes labiatus (mirror image); C, Iaseudosimochromis curvij}-ons (mirror image),

bital (Fig. 2B). Because the anteriormost bone underlay the second bone, these bones are considered as homologous of IOI and I02 of type A, respectively. Simi- 1arly, because the dermosphenotic and preceding bone were tube-like with two sensory pores each, these bones correspond to I06 and I05 of type A, respectively. Ac- cordingly, the single elongated bone between I02 and I05 most likely corresponds to the united I03 and I04 elements of type A. Tylochromini (Fig. IB, Table 1), A single Tanganyikan species is included in this tribe, 7b,lochromispolylopts. The infraorbitals are similar to type A, except fbr the presence of three, not two, sensory pores on the fourth infraorbital, which is the longest of the tube-like infiraorbitals (Fig. IB). The location and length of this bone undoubtedly indicate its correspondence to I04 of type A; therefore, this condition most likely represents a variation of type A, dilifering only in the increased number of sensory pores on I04. Tropheini (Fig. 3, Table 1). Limnotilopia dardennii, Petrochromisfosciolatus, P. polyodon, Simochromis babaulti, S. diagramma, TrQphetts duboisi, and T moorii all have the type A infiraorbital pattern, although I04 is sometimes shorter than I05 (Fig, 3A). The infiraorbitals of most specimens of interochromis loocki and Lobochilotes tabiatus agreed with type A; in one example of each species, however, there were three, not two, sensory pores on I04 (Fig, 3B). In two specimens each of Cblphotilmpia frontosa and Rseudosimochromts curvij}"ons, the infraorbitals agreed with type A. In eontrast, in one spectmen of each species, the infraorbitals numbered only five, with three sensory pores present on an elongated bone located between I02 (which overlapped IOI) and I05 (preceding the dermosphenotic) (Fig. 3C). This condition is considered to be a variation of type A, resulting from the fusion of I03 and I04.

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Imbaorbitals of Tanganyikan cichlids 11

Eretmodini (Fig. 4, Table 1). In al1 examined specimens of this tribe, except one example of Eretmodus cJ,anostictus, the inhaorbitals were similar to those of type A, although the infraorbitals numbered only five and three sensory pores oc- curred on an elongated bone located between I02 (which overlapped IOI) and I05 (preceding the dermosphenotic) (Fig. 4A). These conditions are considered to be a variation of type A, resulting from the fusion of I03 and I04. In one specimen of Eretmodus cyanostictus, the infraorbitals were only four in number, with six sensory pores on the anteriormost bone and three sensory pores on the second bone (Fig. 4B). Six sensory pores and the lack of overlap between the anteriormost and the fo11owing bones suggest that the anteriormost bone corre-

sponds to the fused IOI and I02 elements of type A. The 1ocation ofa second elon-

5mm

Fig. 4. Infiraorbitals of tribe Ectodini. A, Spathodus marlieri; B, Eretmodus cJ,anostictus.

A B

5mm 5mm -

5mm -

Fig, 5. Infiraorbitals of tribe Perissodini. A, Perissodus microlepis; B, Xbnochromis hecqui; C, Haplotaxodonmicrolepis.

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12 Tetsumi Takahashi

gated bone between IOI+I02 and I05 (a tube-like bone preceding the dermosphe- notie) suggests that the former corresponds to the fused I03 and I04 elements, the condition therefore being considered as a variation of type A (IOI+I02, I03+I04). Perissodini (Fig. 5, Table 1). In Perissodus microlapis, Plecodus straeleni, and Xignochromis hecqui, the infiraorbitals are similar to those of type A, but IOI is relatively shal]ow with short marginal canals (Fig. 5A, B). In X hecqui, I04 is short, approximately the same length as I03, and I05 is long, approximately twice the length of I04 (Fig. 5B). These conditions are considered to be variations of type A. in Plecodus paradoxus, the infraorbitals are similar to typical type A exeept fbr the presence of six sensory pores on the anteriormost infraorbital. The overlapping of this bone with the fo11owing tube-like bone suggests that these bones correspond to IOI and I02 of type A; therefbre, these infraorbitals most likely represent a variation of type A, resulting from an increased number of sensory pores on IOI, but without fusion of any bones. in Haplotaxodon microlepis, the inhaorbitals are similar to those of type A, but there are seven of them, not six, and the anteriormost inhaorbital is relatively shallow with short marginal canals (Fig, 5C). The overlap between the anterior- mest bone and the adjacent tube-like bone suggests that these bones correspond to IOI and I02 of type A. The posteriormost bone is dermosphenotic. Therefbre, this condition most likely represents a variation of type A, resulting from an increase in the number of inhaorbitals between I02 and the dermosphenotic. Ectodini (Fig. 6, Table 1). Most species of this tribe show intraspecific variation in the numbers of sensory pores on IOI and I02. In Autonocranus dewindti, Ctzllochromis nzacrops, Cardiqphar:vnx schoutedeni, Cunningtonia tongiventralis, ClyathQpha]lynx.fttrcijler, Ettodus descampsi, Gramma- totria lemairii, Lestradeaperspicax, and Ciphthalmotilopia nasuta, the inhaorbitals number fbur (Fig, 6A, B). IOI is a thin, triangular bone that is more elongated posteriorly than those in any other tribe. The sensory canal on IOI extends to the posterior part of the bone, opening through six sensory pores (seven in one specimen each of dnttochromis macrops and byathQphar:J;nx.furcder). I02-I04 are arranged in a single continuous series. I02 is elongated with four or five sensory pores (six in one specimen each of A. dewindti and E. descampsi) and is anteriorly separated from or touches IOI, but never overlaps the latter. I03 and I04 (dermosphenotic) are short, each with two sensory pores. This condition, herein termed type B, including four infraorbitals, elongated I02, and lack of overlap between IOI and I02, which also have more sensory pores than any of the other types, is restricted to these genera among Tanganyikan cichlids. Iri Xenotilapia species except X laptura, the inhaorbitals are similar to those of type B. However, the sensory canal on IOI is short, not extending to the posterior part of the bone, with the sensory pore number redueed to fbur or five (Fig. 6C, D, E). The length of the sensory canal on I02 varies, being elongated with fbur or five sensory pores and reaching the anterior end of the bone in two specimens ofXL boulengeri (Fig. 6C), but absent in one specimen of X: tenuidentata (Fig. 6E). Other specimens examined showed various intermediate forms (Fig. 6D). These conditions are considered as variations of type B, resulting from a reduction of the sen-

sory canals on IOI. in Xenotilopia lqptura, one specimen exhibited the typical type B condition, and another, a type B variation with a reduced IOI sensory canal.

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Infraorbitals of Tanganyikan cichlids 13

A "

5mm 5mm- -

5mmm D E A

5mm 5mm -

Fig. 6. Infraorbitals of tribe Ectodini. A, Ebtodus descampsi ; B, Cb,athQpharynx fitrcijl?r; C, Xenotilmpia boulengeri; D, X melanogeays; E, X tenuidentata (mirror image).

Liem (1981) and Greenwood (1983) treated the presence of an anteriorly-di- rected angular process on the anterior end of IOI as a synapomorphy of four (Liem) or ten (Greenwood) genera of Ectodini. Such a process was not observed during the present study. In his description of Ectodtts and figures of Cunningtonia, ECtodus, Lestradea, and Ciphthatmotilopia, Liem (1981) indicated that these genera of Ectodini have five to seven well-developed infraorbitals, I02 being short. Although all the genera of Ectodini, collected from various localities in Lake Tanganyika, were examined during the present study, sueh a condition was not fbund and is therefore excluded from consideration here. Re-examinations of Liem's (1981) specimens are necessary in order to resolve this discrepancy. Trematocarini (Fig. 7, Table 1). In T)'ematocara macrostoma and TL unimacu- tatum, the inhaorbitals number five (Fig. 7A). IOI is a thin, rectangular, plate-1ike bone with five sensory pores, I02-I04 are thin, plate-like bones, each with a sensory canal epening through two sensory pores, and I05 is a tube-1ike bone, I02

touches but never overlaps IOI. A dermosphenotic is absent. All of the sensory

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14 Tetsumi Takahashi

5mm '

5mm

Fig. 7. Infraorbitals of tribe Trematocarini. A, 7rematocara macrostoma; B, T. marginatum;

C, T, nigrifrons.

pores are enlarged, adjacent pores being almost in contact. This condition, restricted to these two species among Tanganyikan cichlids, is named type C, ln Trematocara nzarginat"m and T, zebra, the inflraorbitals are similar to type C, aithough numbering only fbur (Fig. 7B). This most likely represents a variation of type C, resulting from the absence of the tube-like I05. The infraorbitals of fll cqparti, T. kujCfl?rathi, 7L nigrij}'ons, T. stigmaticum, and T, variabile are similar to those of type C; however, the inhraorbitals sometimes number only four, and sensory canals are absent on the posteriormost two to four infraorbitals (Fig. 7C). These conditions most likely represent variations of type C. Lamprologini (Fig. 8, Table 1). Most species of this tribe exhibit intraspecific variation in the numbers of infraorbitals and sensory pores. In all species examined except IVeolamprolcrgtts toae and Vtzriabilichromis moorii, the infraorbitals number from one to five (Fig, 8A, B, C). IOI is a rectangular bone with three to seven sensory pores. A tube-1ike dermosphenotic is some- ttmes present, Inhaorbitals between IOI and the dermosphenotic (or between IOI and the usual dermosphenotic position) are sometimes absent, but when present are generally tiny and not tube-1ike in structure, being discontinuously arranged. This condition characterized by conspicuously atrophied infraorbitals is named

type D. In one specimen of Aleolamprologus toae, nine infraorbitals were continuously arranged in a single series (Fig. 8D). IOI was rectangular with four sensory pores, the posterior part underlying I02. I02-I09 (dermosphenotic) were short, tube-like

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Infraorbitals of Tanganyikan cichlids 15 A " a p v (

5mm- mm N/ -

5mm 5mm - E F "

5mm 5mm -

G H g "ijf' !5mm 5mm

Fig. 8, Inflraorbitals of tribe LamprologinL A, Lamprologus lemairii;B,F:Lqpidioiamprologus

prqfttndicota; C, Jttlidochromis ornattts; D-F, IVbolamprologus toae (E, mirror images); G, H, Viririabilichromis moorii (H: mirror image).

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16 Tetsumi Takahashi

bones with two or three sensory pores each. This number of infraorbitals is the highest found among the Tanganyikan cichlids examined, and the condition is

named type E. In five ether specimens of AJic]olarnprolQgus toae, three to six infraorbitals were separated into anterior and posterior groups (Fig. 8E, F). The anterior group in- "IOI" cluded with fbur or five sensory pores and one or two short bones. Because "IOI" with four sensory peres (Fig. 8E) underlay the following bone, these bones are considered to be IOI and I02, respectively. The bone following I02 corresponds "IOI" to I03. 0n the other hand, with five sensory pores (Fig. 8F), being more posteriorly elongated than that with four sensory pores and not underlying the following bone, is considered to represent fused IOI and I02 elements, the following element being I03. The posterior group included one to four bones, the posteriormost bene being the dermosphenotic (I09). In one specimen, I08 was present (Fig. 8E), and in another, I05, I06+I07, and I08 were present (Fig. 8F). In other specimens, the posterior group comprised only the dermosphenotic. All in al1, these various separated inhaorbital series most likely represent variations of type E, resulting from a loss of one to five infraorbitals from the middle of the infraorbital series (I04, I04-I07, or I04-I08, Table 1), Stiassny (1997, fig. 8a) illustrated the infraorbitals of A]botamprologLts toae as consisting of eight elements; there were five sensory pores on the anteriormost element, which failed to underlie the following tube-like bone. This condition most likely represents another variation of type E, resulting from the fusion of IOI and I02. in Viczriabilichromis moorii, the infraorbitals number fbur (Fig. 8G, H), the anteriormost being rectangular with either five or six sensory pores, Three moderately long bones with two sensory pores each are arranged in a single continuous

5mm'

Fig. 9. Infraorbitals of tribe Bathybatini.A, Bath),bates graueri (mirror image); B, B. minor;

C, Hemibates stenosoma.

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Imbaorbitals of Tanganyikan cichlids 17

series, that is widely separated from the anteriormost inhaorbital. The posteriormost infraorbital is the dermosphenotic. The anteriormost infraorbitals with five (Fig, 8G) and six (Fig. 8H) sensory pores appear to represent IOI and IOI+I02 of type A, respectively, and the tube-like bones apparently represent I04-I06, The gap between the anteriomiost bone and the tube-like bones may have resulted from the loss of I02 and I03 (Fig. 8G), or just I03 (Fig. 8H), of type A. Bathybatini (Fig. 9, Table 1), In Batdybatesfosciatus and B. graueri, the infraorbitals number six (Fig. 9A), IOI being a rectangular bone with five sensory pores, Three moderately elongated marginal canals on IOI, extendtng downward, have their dorsal walls notched deeper than half-length of the canal. I02-I06 are tube-like bones arranged in a single continuous series, with two sensory pores each. I02-I05 are approximately the same length, and I06 (dermosphenotic) is the shortest among the tube-like bones. The presence of notched marginal canals on IOI is unique to these two species among Tanganyikan cichlids, and this condition

is named type F. in Batbybates nzinor, the infraorbitals are similar to type F, except for the presence of eight infraorbitals and six sensory pores on IOI (Fig. 9B). As in type F, there are deeply notched marginal canals on IOI; therefore, the larger numbers of infraorbitals and sensory pores on IOI in this species most likely represent a variation of type F. Homologous elements could not be identified between this species and B. fctsciatus and B graueri, In Hemibates stenosoma, the infraorbitals are similar to those of type A, except for their lengths, I02 tending to be elongated and the same length as or longer than I04 (Fig. 9C). This condition was not clearly separable firom the typical type A condition, because of the presence of intraspecMc variation in the lengths of the tube- like infraorbitals. Limnochromini (Fig. 10, Table 1). The infraorbitals of Gnathochromis ptfeXTIiri are in accordance with type A (Fig. 10A). In Greenwoodochromis christyi, the infraorbitals are similar to those of type A except for the presence of six, not five, sensory pores on the anteriormost infraorbital (Fig. 10B). The overlap between this bone and the adjacent tube-like bone suggests that these bones correspond to IOI and I02 of type A. Therefore, this condition most likely represents a variation of type A, resulting from an increase in the number of sensory pores on IOI, but without any fusion of bones. In Benthochronzis tricoti, the inhaorbitals are similar to type A except for the presence of seven inhaorbitals instead of six (Fig. 10C). The overlap between the anteriormost bone and the adjacent tube-like bone suggests that these bones correspond to IOI and I02 of type A. The posteriormost bone is dermosphenotic. There- fore, this condition most likely represents a variation of type A, resulting from an

increase in the number of infraorbitals between I02 and the dermosphenotic, in Gnathochromis permaxitlaris, Raganochrontis calliurus, 1kengachromis dhanisi, Triglachromis otostigma, and one examined speeimen of Baileychromis centropomoides, the infiraorbitals number three (Fig. 10D, E), IOI being a triangular or elongated rectangular bone with five (six in one specimen of T otostigma) sensory pores, and I02 and I03 being arranged in a singte continuous series. I02, an elongated, tube-like bone with four to six sensory pores, anteriorly never overlaps IOI, I03 (the dermosphenotic), a short, tube-like bone, possesses two sensory pores. This condition, a total of three tnfraorbitals, with I02 elongated and having

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18 Tetsumi Takahashi

' -

- -

E F

5mm 5mm -

Fig. 10. Infiraerbitals of tribe Limnochromini. A, Gnathochromts ptfllfferi; B, Greenwood- ochromis christyi (mirror image); C, Benthochromis tricoti; D, Gnathochromis permaxillaris; E, Ttzngachromis dhanisi; F, Bailqychromis centrQpomoides.

a 1arge number of sensory pores but not overlapping IOI, is distinctive among Tan- ganyikan cichlids and is named type G. The other examined specimen ef Bailaychromis centropomoides differed from type G by having four infraorbitals (Fig, 10F). Beeause the anteriormost infraor- 'Ihe bital was plate-like with five sensory pores, it corresponds to IOI of type G, posteriormost element corresponds to I03 of type G, namely, the dermosphenotic. Whereas in type G the elongated bone between IOI and I03 has sensory pores arranged at irregular intervals with the posterior two intervals tending to be wider than the anterior intervals, in the present specimen two infraorbitals were present between IOI and I03. The anterior bone was short with four sensory pores, the other long with three sensory pores, The tnter'vals between the sensory pores

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Infraorbitals of Tanganyikan cichlids 19

A ) {i(2i

5mm 5mm - c D B

5mm 5mm - -

Fig. 11. Infraorbitals of tribe Cyprichromini. A, dyprichromis lqptosoma; B, C. microlepidotus;

C, D, Paracyprichroniis brieni.

on the anterior bone were narrower than those on the posterior element, indicating that these bones correspond to the anterior and posterior parts of I02 of type G. Although Linznochromis auritus was not examined in the present study, its infraorbitals apparently correspond to type G, accordtng to an illustration in Sti- assny (1997, fig. 10d): five sensory pores on IOI, five sensory pores on elongated I02, and two sensory pores on I03. Cyprichromini (Fig. 11, Table 1). The infraorbitals of byprichromis tqptosoma are similar to type A except for the presence of seven, not six, inhaorbitals and a triangular anteriormost bone (Fig. 11A). The overlap between the anteriormost bone and the adjacent tube-like bone suggests that these bones correspond to IOI and I02 of type A. The posteriormost bone is dermosphenotic. Therefore, this condition most likely represents a variation of type A, resulting from an increase in the number of infraorbitals between I02 and the dermosphenotic. The infraorbitals of (]blprichromis microlepidotus are similar to those of type A, but IOI is triangular and I02 and I03 are elongated, being approximately the same length as I04 (Fig. 11B). This condition is considered as a variation of type A. In Paraqyprichromis brieni, the infraorbitals number six or seven (Fig. 11C, D). IOI is a triangular bone with four or five sensory pores. I02-dermosphenotic (I06 or I07) are arranged in a single continuous series. I02 is a smal1 bone lacking a sensory canal and anteriorly overlapping IOI. I03 is also small with an incomplete sensory canal that is open posteriorly but closed anteriorly. I04-dermosphenotic are tube-1ike bones with two sensory pores each. In two speeimens, the tube-like bone preceding the dermosphenotic was elongated with three sensory pores (Fig, 11D). This bone is considered to represent the fusion of I05 and I06. Although intraspecific variation occurs in the numbers of infraorbitals and sensory pores on

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20 Tetsumi Takahashi

IOI, and in the fusion of I05 and I06, they all are included in a single type H, be-

cause they share unique condition among Tanganyikan cichlids: the sensory canal being absent on I02 and anteriorly closed on I03. Homologous elements could not be identified between the infraorbital series with six and seven elements.

Discussion

A comparison of the higher level categories of Lake Tanganyikan ciehlids based on inhaorbital arrangement and the tribal level classification proposed by Poll (1986) shows that each of eight nibes is represented by a monotypic infraorbital condition, vix. Tilapiini, Haplochromini, Tylochromini, Tropheini, Eretmo- dini, and Perissodini (type A), Ectodini (type B), and Trematocarini (type C). The other four tribes each have two or three types of infraorbital array, viz. Lampro- logini (types A, D, and E), Bathybatini (types A and F), Limnochromini (types A and G), and Cyprichromtni (types A and H). Type A infraorbitals have already been inferred to represent the ancestral condition fbr African cichlids (Stiassny 1997). They occur in about half of the Tan- ganyikan cichlid genera. Variations of type A, such as fusion oftwo adjacent infraorbitals and increase in number of sensory pores without fusion of imbaorbitals, were found in difiierent tribes: fusion of infraorbitals in Astatotilopia burtoni and Ctenochromis benthicola (Haplochromini), Cb7photilmpia frontosa and 1:lseudosi- mochromis curvip"ons (Tropheini), Eretmodus qyanostictus, Eipathodus marlieri, and 7Zinganicodus irsacae (Eretmodini), and VZxriabilichromis moorii (Lampro- logini); and increase in sensory pores in Ttylochromispolylepis (Tylochromini), interochromis loocki and Lobochilotes tabiatus (Tropheini), Greentvoodochromis christyi (Limnochromini), and Plecodus paradoxus (Perissodini), The infraorbital series of most of these species exhibits both the typical and variant conditions of type A in different individuals; accordingly, such variations are considered to have developed separately in each species (parallel development), Type B infraorbitals were fbund in all examined Ectodini, but never in other tribes. The tribe Ectodini has been inferred to be a monophyletic group on the basis of both morphological (Greenwood 1983; Takahashi 2003) and molecular (Sturmbauer and Meyer 1993; Nishida 1997; Takahashi et al. 1998) analyses, and the type B infraorbital condition can be considered as a synapomorphy of this tribe (also see Takahashi 2003, fig. 6), Furthermore, a variation of type B, sensory canal on IOI being short with four or five sensory pores, is a synapomorphy supporting the monophyly of Xenotilqpia (Takahashi 2003). Type C infkraorbitals have a[Lready been treated as a synapomorphy of the tribe Trematocarini on the basis of the morphological phylogeny (Takahashi 2002). The monophyly of this tribe has otherwise been supported by the presence of tendon "c" of adductor mandibulae section 1, a single scale row between the upper }ateral line and body axis, and the absence of lower Iateral 1ine (Takahashi 2002). The monophyly of the tribe Lamprologini has been supported by both morphological (Stiassny 1997) and moleeular (Sturmbauer et al. 1994; Nishida 1997; Taka- hashi et al. 1998) evidence. With the exception of ATeolamprolcrgus toae, reduced infraorbitals have been reported as a synapomorphy or diagnostic character of Lam- prologini by Colombe and Allgayer (1985), Poll (1986), and Stiassny (1997). Stiassny

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Infraorbitals of Tanganyikan cichlids 21

(1997) explained the reduction in infiraorbitals number in Lamprologini as the re- sult of bone loss, rather than fusion. This idea is supported here, because the infraorbitals fo11owing IOI are either absent or very small and discontinuously arranged (Fig. 8A-C), quite unlike the fused infraorbitals of some other Tan- ganyikan cichlids, which are elongated with three sensory pores (Figs 2B, 3C, 4A, B). in AJeolamprolQgus toae, Stiassny (1997) reported seven or eight infraorbitals, which differed from the reduced, discontinuous imbaorbital series seen in other taxa of Lamprologini (type D of the present study). However, she did not exclude the former from Lamprologini for two reasons: other morphological features of N toae matched those of other lamprologine species and the molecular phylogeny of Sturmbauer et al. (1994) tncluded this species in the Lamprologini flock. Stiassny (1997) could not comment on the phylogenetic status of the infraorbital configuration in this species, because she had been unable to examine any specimens of N qylindricus, which had been placed as the sister group of Ait toae in the molecular tree (Sturmbauer et at. 1994). The present study found IVL toae alone among Lam- prologini to have nine infraorbitals (type E, Fig, 8E), the 1argest number among the Tanganyikan cichlids examined, whereas N qylindricus had only IOI, as in most Lamprologini. Although some elements of IVL toae appeared to represent loss and/or fusion, its inhaorbital condition is judged to be an autapomorphy for the specles.

Among the Lamprologini, only VZzriabilichromis rnoorii appears to have type A infraorbitals (the plesiomorphic condition for African cichlids), atthough some elements had been lost. This strengthens the suggestion that Vl nzoorii be placed in the most basal position among Lamprologini, as proposed by Sturmbauer et al. (1994) and Stiassny (1997). As discussed above, the monophyly of the clade including other Lamprologini besides Vl moorii i's supported by the presence of type D in-

fraorbitals, with the exception of AL toae, which has an autapomorphic infraorbital condition (type E). The tribe Bathybatini includes species showing two diflierent infraorbital types, i.e, type A (Hemibates stenosoma) and type F (Batbybates species). Among the Tanganyikan cichlids examined, a notched dorsal wall of the marginal canal on IOI (type F) was fbund only in the genus Batbybates. The monophyly of Batdy- "a" bates has otherwise been supported by the presence of a short tendon of adductor mandibulae section 1 and the well developed maxillary flange on which tendon "a" is inserted (Stiassny 1981). Examination of other species of Bathybates unavail- able during this study (B. .ferox Boulenger, 1898, B. horni Steindachner, 1911, B. Ieo Poll, 1956, and B. vittatus Boulenger, 1914) is necessary to determine the status of type F and whether or not it represents a synapomorphy of the genus. The tribe Limnochromini includes species with two inflraorbital types, i.e. type A (Benthochromis tricoti, Gnathochromts pLfeXXieri, and Greenwoodochromis christyi) and type G (Baileychromis centrQpomoides, Gnathochromis perrnaxillaris, Limnochronzis auritus, Raganochromis calliurus, 71angachronzis dhanisi, and Triglachromis otostigma). Among the Tanganyikan cichlids examined, type G in-

fraorbltals were found only in the above six taxa, and this fact suggests that they might represent a monophyletic group. On the other hand, according to the molecular phylogeny of Nishida <1997), this group is not monophyletic, G. permaxillaris being placed far from a clade comprising L. auritus and 71 otostigma. However,

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22 Tetsumi Takahashi

this relationship is not well established because of very low bootstrap values. The tribe Cyprichromini includes species with two infraorbital types, type A ((lyprichromis species) and type H (Paracyprichromis brieni). Examination of the only congener of P. brieni, P, nigrij}"ons (Boulenger, 1901), was not possible during this study, so it is whether type H is an autapomorphy of P. brieni or a synapomorphy of the genus.

Summary

The infraorbitals of Tanganyikan cichlids can be classified into eight types, as summarized in Table 2. Type C is easily recognized by the presence of extremely well-developed sensory pores on plate-like imbaorbitals, the adjacent pores being almost in contact, and by the absence of the dermosphenotic. Type D is also clearly separable from other types by the atrophied state of the infraorbitals between IOI and the dermosphenotic (or usual dermosphenotic position); they are either absent or tiny, lack a tube-like structure, and are discontinuously arranged. The other types all possess a dermosphenotic. Types B and G resemble each other in having an elongated, tube-like I02 that does not overlap IOI, but these types are separable by the number of infraorbitals: four in type B, three in type G (I02 of type G is on rare occasions separated into two elements, increasing the number of infraorbitals to fbur, but such differs from type B insofar as the anterior element is shorter than the posterior element). Type F is characterized by deep notches in the dorsal wall of the marginal canals on IOI. Type H is unique in having the sensory canal absent on I02, and that on I03 closed anteriorly. Type E is unique, being represented by up to nine inhraorbitals; some infraorbitals located between I03 and the dermosphenotic are usually lost, forming a discontinuously arranged series, and in addi- tion, IOI and I02 are sometimes fused. Type A basically has six infraorbitals with five sensory pores on IOI and two each on I02-I06. In this type, some variations are occasionally found: two adjacent infraorbitals, excluding the dermosphenotic, being fused and forming an elongated bone with three sensory pores (or six sensory pores, when IOI and I02 are fused); sensory pores increastng to six on IOI or three on I04, without fusion of any inhaorbitals; one or two tube-1ike infraorbitals lost; I02 and!or I03 elongated; or infraorbitals increasing to seven. These variations seldom occur simultaneously in a single infraorbital series. Tilapiini, Haplochromini, Tylochromini, Tropheini, Eretmodini, and Perisso- dini all type A, which has been treated as a plesiomorphy for African cichlids. The monophyly of Eetodini and Trematocarini was supported by types B and C, which can be regarded as synapomorphies of these two tribes, respectively. The monophyly of Lamprologini, except Viczriabilichromis moorii, was supported by type D, on apparent synapomorphy, the single exceptton being Areolamprologus toae, which had type E infraorbitals as an autapomorphy for the species; V moorii should be placed at the most basal position within the Lamprologini clade on the basis of having a variation of type A infraorbitals. The phylogenetic significance of types F, G, and H remains unresolved.

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11血 aorbitals of Tanganyikan cichlids 23 −

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24 Tetsumi Takahashi

Acknowledgements

I express my sincere thanks to Dr. Kunio Amaoka (formerly HUMZ), PreE Kazuhiro Nakaya (HUMZ), and Assistant Prof. Hisashi Imamura (The Hokkaido University Museum) for their valuable advice and the lean of specimens, to Drs Guy G. Teugels and Jos Snoeks (MRAC) and Drs William L. Fink and Douglas W. Nelson (UMMZ) for the loan of specimens, to Pro £ Michio Hori and Dr. Ken Watan- abe (Kyoto University), Prof. Kosaku Yamaoka (Kochi University), Dr. Katsuki Nakai (LBM), Dr. Masta J. B. Gashagaza (Environmental Research Development, Rwanda), and Dr, Haruki Ochi (Ehime University) for the collection and gift of specimens, to Dr. Graham S. Hardy (Nguriguru, New Zealand) for his advice and comments on the manuscript, and to Messrs Mitsuto Aibara (HUMZ) and Yuya Fu- ruyama (fbrmerly HUMZ) for their kind assistance. This study was partly supported by a Grant-in-Aid for Overseas Scientific Survey (No. 04041078 and 10041178) from the Ministry of Education, Science, Sports and Culture, Government of Japan.

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