Neolamprologus

Piet Verburg & Roger Bills, 2007, Two new cichild species Neolamprologus (Teleostei: Cichlidae) from Lake Tanganyika, East Africa., Zootaxa 1612, pp. 25-44 : 39-41

[[ Genus Neolamprologus ]]

Key to the species of the Neolamprologus savoryi complex

1 Marks on operculum .................................................................................................................................... 2

- Opercular marks absent .............................................................................................................................. 8

2 V-shaped mark with bright spot on operculum,>35 scales in the longitudinal line .................................... 3

- Opercular mark not V-shaped, <35 scales in the longitudinal line ..............................................................4

3 Opercular spot red, scales on paired fins, ctenoid scales on anal and dorsal fins ...................... N. splendens

- Opercular spot yellow, no scales on paired fins, cycloid scales on anal and dorsal fins .......... N. helianthus

4 Twelve soft rays in pectoral fin, anal fin filament longer than of dorsal fin, headlength> 34 %SL, 3 scales between lateral lines, bars on body ................................................................................................ N. savoryi

- Thirteen soft rays in pectoral fin, anal fin filament shorter than of dorsal fin, headlength <34 %SL, 2 scales between lateral lines, no bars ............................................................................................................ 5

5 Cephalic pits, cheek depth> 28 % HL, opercular mark vague ..................................................... N. crassus

- Cephalic pits absent, cheek depth <28 % HL, opercular marks distinct .................................................... 6

6 No conspicuous spots on scales, no yellow border under eye, caudal peduncle length>18 %SL ................ .................................................................................................................................................... N. brichardi

- Conspicuous spots on scales, yellow border under eye (white in preserved specimens), caudal peduncle length <18 %SL ........................................................................................................................................... 7

7 Scales between pectoral fin and pelvic fin, and between dorsal fin origin and lateral line clearly visible, rows of spots on scales regular ..................................................................................................... N. pulcher

- Same scales deeply embedded and not always clearly visible, rows of spots on scales irregular, with interruptions..................................................................................................................................... N. olivaceous

8 No scales on occiput, few scales on nape .................................................................................................... 9

- Few scales on occiput, many scales on nape.............................................................................................10

9 Distinct black and white marginal bands on dorsal and caudal fin and striped pattern on unpaired fins, preorbital depth <17 % HL, eight to fifteen scales on operculum.................................................... N. walteri

- Faint markings and no distinct black and white marginal bands on unpaired fins, preorbital depth> 17 % HL, 12-30 scales on operculum.................................................................................................. N. falcicula

10 Scales around caudal peduncle> 17, gill rakers> 15, 3 scales between lateral lines.................. N. gracilis

- Scales around caudal peduncle <17, gill rakers <10, 2 scales between lateral lines...............................11

11 Body depth <29 % SL, headlength> 30 % SL, inter orbital width <25 % HL, caudal peduncle length/ depth ratio>1.25, no scales on unpaired fins and cycloid scales on dorsal and anal fins................... N. chitamwebwai

- Body depth> 29 % SL, headlength <30 % SL, inter orbital width> 25 % HL, caudal peduncle length/ depth ratio <1.10, scales on unpaired fins and ctenoid scales on dorsal and anal fins................. N. marunguensis

Discussion

Seehausen et al. (1998) noted in cichlids of the rocky shores of Lake Victoria that while sympatric congenerics differed in male coloration, less closely related sympatric cichlids often did not differ in male coloration. Seehausen et al. (1998) suggested that the differences in male coloration are needed to maintain reproductive isolation between close relatives. There is no sexual dimorphism in the species of the N. savoryi complex, and reproductive isolation between these sympatric close relatives is apparently maintained by a different mechanism. The fewer and less obvious differences between N. walteri and N. chitamwebwai compared with differences with N. savoryi and N. brichardi suggest that the former couple is more closely related. It seems plausible that in N. walteri and N. chitamwebwai ecological differentiation is key to the maintenance of reproductive isolation.

The two new species although closely related, show clear ecological differentiation. Due to habitat isolation, N. walteri and N. chitamwebwai did not occur in exactly the same areas, but were separated by no more than 4 (on the south side of Cape Bangwe) to several hundred metres (on the north side of Cape Bangwe where sandy beaches interrupt the rocky shores and neither species occur). The two new species can therefore be considered sympatric. Stable isotope data (13C, 15N) showed no overlap of diet between N. walteri , N. chitamwebwai and N. brichardi and little overlap of N. chitamwebwai with N. savoryi (Verburg & Hecky, unpublished data). 13C data of N. walteri were intermediate between the high values of N. chitamwebwai and N. savoryi (high 13C indicating a more benthic diet) and the low values of N. brichardi (low 13C indicating a more planktivore diet, Verburg & Hecky, unpublished data).

In sympatric fish species pairs often one will be a benthic feeder while the other specializes on pelagic food sources (Schliewen et al., 1994; Schluter, 2000). Ecological differentiation may be related to morphological differences between species in the complex. Differences in head measures and their allometric coefficients as found between N. walteri and N. chitamwebwai (Fig. 5B) may be related to the method of preyhandling (Wilhelm, 1984). As shown by Wilhelm (1984; compare Fig. 5B), it is not only variation in body size together with allometry that accounts for variation in head morphology between cichlid species. Both N. chitamwebwai and N. savoryi , the two species with the most benthic diet according to stable isotope data, have smaller cheek depths than the other species in the complex (Fig. 5B). The teeth in the posterior row on the lower pharyngeal bone of N. chitamwebwai (Fig. 7) while resembling those of N. savoryi (Poll, 1949) are slightly larger than of N. walteri , and especially N. brichardi (Trewavas & Poll, 1952) , possibly related to a more benthic diet of N. chitamwebwai and N. savoryi while N. brichardi feeds on zooplankton (Konings, 1998). In addition, N. brichardi has more gill rakers (11-16) than does N. walteri (6-11) and N. chitamwebwai (6-9), which agrees with a more pelagic diet of N. brichardi . However, several morphological differences found between N. chitamwebwai , N. walteri and N. brichardi contrast with what would be expected from a more benthic diet of N. chitamwebwai compared with N. walteri and N. brichardi . The number of gill rakers did not differ between N. chitamwebwai and N. walteri , and the small body depth and the longer and less steep ascending process of the premaxilla (Fig 6) of N. chitamwebwai are considered to be more typical for pelagic planktivorous fish (Day et al., 1994; Meyer, 1987). However, while the members of the N. savoryi complex may differ in the benthic versus pelagic proportions of their diets, they are all littoral species that do not migrate from the rocky shores, including the planktivore N. brichardi , and are rarely seen more than 1 m away from the bottom. Therefore interspecific morphological differences related to the way of feeding are probably less evident than those often seen between other species pairs of which one is benthic and the other truly pelagic (Robinson & Wilson, 1994).

Evidence of ecological differentiation between closely related sympatric cichlids is rare in literature. Closely related sympatric cichlids in the large African lakes (with literature mainly referring to Lake Victoria and Lake Malawi) have been considered to differ little in diet and habitat use, encouraging the idea that cichlids can coexist without niche partitioning (Coyne & Orr, 2004). Coyne & Orr (2004) suggested that studies of ecological differentiation in closely related sympatric cichlid species are badly needed to test this idea. While there have been several studies that showed ecological differentiation between closely related sympatric cichlids in Lake Victoria (Goldschmidt et al., 1990; Goldschmidt & Witte, 1990; Witte, 1984), our paper suggests a new opportunity to examine ecological differentiation in two new closely related sympatric cichlid species from Lake Tanganyika.