Community ecology and conservation of the fishes of the Okavango Delta, Botswana

Merron, Glenn S.; Bruton, Michael N.

doi:10.1007/bf00002478

Cited by 40 publications

(51 citation statements)

References 6 publications

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“…Like in many other mormyrid species (Iles, 1960), males are recognised by a kink in the anal fin base which is straight in females (Skelton, 2001;Kramer, 1997a,b We included the Okavango specimens in the study because Kramer et al (2007) could not find sexually dimorphic EODs in males of this popula-tion of M. altisambesi in the field on 21-24 January 2001, raising suspicion as to their species identity. This turned out to be groundless: the flood pulse from the Angolan Highlands arrives in the Okavango delta only in March/April (Merron & Bruton, 1995); additional gene sequence analyses confirmed there was no noticeable differentiation between the two populations (M. Wink, personal communication).…”

Section: Fish and Their Carementioning

confidence: 99%

“…The absence of long male EODs in January 2001 ) that caused concern is most likely due to a delayed flood, hence breeding season. Although January is technically in local 'summer', the flood following rainfall in the Angolan mountains arrives in the Okavango delta region only in April-March (Merron & Bruton, 1995). Correspondingly, the long male EODs of Zambezi specimens from Caprivi were sampled in March (Kramer, 1997a,b).…”

Section: Experimental Female Subjectsmentioning

confidence: 99%

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Intra- versus inter-sexual selection in the dimorphic electric organ discharges of the snoutfish Marcusenius altisambesi (Mormyriformes, Teleostei)

Machnik

Markowski

Krämer

2010

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SummaryMarcusenius pongolensis (South Africa) and M. altisambesi (Upper Zambezi/Okavango) differ in the sex difference of their electric organ discharges (EODs). It is permanent and graded in the former and seasonally dimorphic in the latter. Four out of six experimental female M. altisambesi gave significantly stronger responses to the long playback EODs of breeding males rather than short EODs, whereas four of seven experimental males responded in the opposite way (with one exception in association time). When re-tested after a year, the female preference for long EODs had vanished. Both sexes discriminated between playback EODs as either long or short (unlike M. pongolensis), with the cutoff between 1420 and 2470 μs (female EOD average, 350 μs). Exposure to social stimuli from tank neighbours of both sexes did not induce growth of EOD duration in males (unlike M. pongolensis). We suggest that in M. altisambesi the sexually dimorphic male EOD has evolved under female (inter-sexual) selection (in M. pongolensis, both inter-and intra-sexual selection); that there is no evidence for male-male competition (intra-sexual selection, present in M. pongolensis); that ecological differences between a floodplain (M. altisambesi) and a more riverine (M. pongolensis) species may be at the origin of the differentiation.

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Section: Fish and Their Carementioning

confidence: 99%

Section: Experimental Female Subjectsmentioning

confidence: 99%

Intra- versus inter-sexual selection in the dimorphic electric organ discharges of the snoutfish Marcusenius altisambesi (Mormyriformes, Teleostei)

Machnik

Markowski

Krämer

2010

Behav

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“…The permanently flooded areas in the Delta constitute important refugia for many of the fish species (Merron and Bruton, 1995), including the commercially important cichlids. However, the pattern of usage of the seasonally flooded areas for breeding and forage (Merron and Bruton, 1995) indicates that there is likely to be a significant flow of nutrients from the seasonally to the permanently flooded areas.…”

Section: Trophic Linkagesmentioning

confidence: 99%

Scenarios of the impact of local and upstream changes in climate and water use on hydro-ecology in the Okavango Delta, Botswana

Murray-Hudson

Wolski

Ringrose

2006

Journal of Hydrology

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“…At unpredictable times in our laboratory, several snoutfish species from the same general region, including the South African sibling species M. pongolensis, have successfully bred and reared young ones. Rather than time of year, ecological cues such as the (rather unpredictable) arrival of the annual flood from the Angolan mountains seem to be relevant (Merron and Bruton 1995). Among the present group of M. altisambesi, courtship and spawning postures have been recorded in our laboratory (Lamml and Kramer 2007).…”

Section: Discussionmentioning

confidence: 77%

Novel electrosensory advertising during diurnal resting period in male snoutfish, Marcusenius altisambesi (Mormyridae, Teleostei)

Machnik

Krämer

2010

J Ethol

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During the day, weakly electric snoutfish, such as Marcusenius altisambesi from the Okavango delta, avoid visually oriented predators by hiding in sheltered, dark places where they discharge their electric organs at a low and variable rate, interspersed with occasional short bursts (mean discharge rate, 4-12 Hz). Hence, histograms of inter-discharge intervals (IDI) are broad and bimodal (IDI range, about 15-500 ms; ''variable IDI pattern''). We report here that with a female neighbor in electrical communication reach, captive males of M. altisambesi (N = 4) each showed a novel type of IDI resting pattern that was characterized by a higher and more constant discharge rate (16-28 Hz). These IDI histograms were unimodal and narrow (IDI range, about 11-100 ms; ''regularized IDI pattern''). In each of these males, the regularized pattern vanished when the female neighbors were replaced by males, and the common variable IDI pattern of low rate was observed instead. In an unforced choice paradigm, six M. altisambesi experimental females were allowed to choose between two electric fish decoys, one playing back the novel regularized IDI pattern and one playing back the variable IDI pattern. Five experimental females significantly preferred staying close to the decoy playing back the regularized IDI pattern, whereas one female showed the opposite preference. It appears that males advertise to females during their diurnal period of overt inactivity, with an inconspicuous signal that neither threatens conspecifics nor alerts predators by overt behavior. A secondary function of the regularized male IDI pattern could be to advance the reproductive cycle of females.

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Community ecology and conservation of the fishes of the Okavango Delta, Botswana

Cited by 40 publications

References 6 publications

Intra- versus inter-sexual selection in the dimorphic electric organ discharges of the snoutfish Marcusenius altisambesi (Mormyriformes, Teleostei)

Intra- versus inter-sexual selection in the dimorphic electric organ discharges of the snoutfish Marcusenius altisambesi (Mormyriformes, Teleostei)

Scenarios of the impact of local and upstream changes in climate and water use on hydro-ecology in the Okavango Delta, Botswana

Novel electrosensory advertising during diurnal resting period in male snoutfish, Marcusenius altisambesi (Mormyridae, Teleostei)

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