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2022 ◽  
Author(s):  
Anna Duenser ◽  
Pooja Singh ◽  
Laurene Alicia Lecaudey ◽  
Christian Sturmbauer ◽  
Craig Albertson ◽  
...  

Studying instances of convergent evolution of novel phenotypes can shed light on the evolutionary constraints that shape morphological diversity. Cichlid fishes from the East African Great Lakes are a prime model to investigate convergent adaptations. However, most studies on cichlid craniofacial morphologies have primarily considered bony structures, while soft tissue adaptations have been less intensely scrutinised. A rare example of an exaggerated soft tissue phenotype is the formation of a snout flap. This tissue flap develops from the upper lip and has evolved in only one cichlid genus from Lake Malawi and one genus from Lake Tanganyika. To investigate the molecular basis of snout flap convergence, we used mRNA sequencing to compare two species with snout flap (Labeotropheus trewavasae and Ophthalmotilapia nasuta) to their close relatives without snout flaps (Tropheops tropheops and Ophthalmotilapia ventralis) from Lake Tanganyika and Malawi. Our analysis revealed a greater complexity of differential gene expression patterns underlying the snout flap in the younger adaptive radiation of Lake Malawi than in the older Lake Tanganyika radiation. We identified 201 genes that were repeatedly differentially expressed between species with and without the snout flap in both lakes, suggesting that the pathway that gives rise to snout flaps is evolutionarily constrained, even though the flaps play very different functions in each species. The convergently expressed genes are involved in proline and hydroxyproline metabolism, which have been linked to human skin and facial deformities. Additionally, we also found enrichment for transcription factor binding sites upstream of differentially expressed genes such as members of the FOX transcription factor family, especially foxf1 and foxa2, which also showed an increased expression in the flapped snout and are linked to nose morphogenesis in mammals, as well as ap4 (tfap4), a transcription factor showing reduced expression in the flapped snout with an unknown role in the development of craniofacial soft tissues. As genes involved in cichlids snout flap development are associated with many human mid-line facial dysmorphologies, our findings imply a conservation of genes involved in mid-line patterning across vastly distant evolutionary lineages of vertebrates.


2022 ◽  
pp. 354-374
Author(s):  
Renalda N. Munubi ◽  
Hieromin A. Lamtane

Over the last century, water temperatures in Lake Tanganyika have risen due to climate change, which increased thermal stratification and reduced the magnitude of nutrient availability. A rise in temperature increases the C:N:P ratio resulting in a poor algal diet. In addition, lake littoral habitat is experiencing increased sediment load due to deforestation of the watershed caused by anthropogenic activities. Sediments cover benthic algae and reduce its nutritional value, consequently affecting the foraging behavior, distribution, and growth performance of algivorous fish. Algae and algivorous fish are an important link in the lake food chain; therefore, if the rise in temperature will continue as predicted, then this may have a cascading effect for the rest of the community in the food chain including human being. This, in turn, may contribute to food insecurity at local and regional levels. To counteract this adaptation and mitigation measures such as environmental monitoring systems and creating new opportunities should be considered.


Animals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 3578
Author(s):  
Maarten P. M. Vanhove ◽  
Raquel Hermans ◽  
Tom Artois ◽  
Nikol Kmentová

Unlike their marine counterparts, tropical freshwater clupeids receive little scientific attention. However, they sustain important fisheries that may be of (inter)national commercial interest. Africa harbours over 20 freshwater clupeid species within Pellonulini. Recent research suggests their most abundant parasites are gill-infecting monogenean flatworms within Kapentagyrus. After inspecting specimens of 12 freshwater clupeids from West and Central Africa, mainly sourced in biodiversity collections, we propose 11 new species of Kapentagyrus, which we describe using their haptoral and genital morphology. Because of their high morphological similarity, species delineation relies mostly on the morphometrics of anchors and hooks. Specifically, earlier, molecular taxonomic work indicated that the proportion between the length of the anchor roots, and between the hook and anchor length, is diagnostic. On average, about one species of Kapentagyrus exists per pellonuline species, although Pellonula leonensis harbours four species and Microthrissa congica two, while Microthrissa moeruensis and Potamothrissa acutirostris share a gill monogenean species. This study more than quadruples the number of known species of Kapentagyrus, also almost quadrupling the number of pellonuline species of which monogeneans are known. Since members of Kapentagyrus are informative about their hosts’ ecology, evolutionary history, and introduction routes, this enables a parasitological perspective on several data-poor African fisheries.


2021 ◽  
Author(s):  
Haixiang Mao ◽  
Andrew Cohen ◽  
Nur Sabrina Rosli ◽  
Michael McGlue ◽  
Murtadha Malallah

2021 ◽  
pp. 281-308
Author(s):  
Annie B. Hore
Keyword(s):  

2021 ◽  
Vol 154 (3) ◽  
pp. 351-361
Author(s):  
Christine Cocquyt ◽  
Pierre-Denis Plisnier ◽  
N’sibula Mulimbwa ◽  
Muderhwa Nshombo

Background and aims – Massive algae growth resulting in a phytoplankton bloom is a very rare event in the meromictic and oligotrophic Lake Tanganyika. Such a bloom was observed in the north of the lake in September 2018. Phytoplankton species composition during this bloom is compared to a documented bloom in 1955, and to the composition in September 2011–2013. Meteorological observations suggest hydrodynamics could explain the occurrence of the 2018 bloom.Material and methods – Phytoplankton net samples were taken in the pelagic and littoral zone near Uvira during five consecutive days of the bloom in 2018. For the period 2011–2013, quantitative phytoplankton samples were obtained during a weekly sampling at the same sites. Samples were analysed with an inverted microscope and relative abundances of the algal species were compared. Key results – Dolichospermum flosaquae (Cyanobacteria) initially dominated the bloom followed by high relative abundance of Limnococcus limneticus (Cyanobacteria) on the third sampling day in September 2018. In the pelagic zone an increase of Nitzschia asterionelloides (Bacillariophyta), and Dictyosphaerium and Lobocystis (Chlorophyta) was observed while in the littoral zone increasing abundances of dinophytes were noted. Dolichospermum flosaquae was also responsible for the bloom reported in 1955, but was only sporadically observed in the 2011–2013 samples. Although Limnococcus limneticus was present in 2011–2013, it never reached relative abundances as high as during the 2018 bloom. Meteorological data indicate that 2018 experienced different conditions compared to previous years: strong south-east winds from May to September with a more eastern direction of the wind, and a well-marked drop in atmospheric pressure between August and September.Conclusion – After a very windy season, the combination of strong hydrodynamics, calmer lake conditions, and high solar radiation and air temperature in September 2018 was favourable for a massive Cyanobacteria bloom in the north of Lake Tanganyika.


Author(s):  
Maarten P.M. Vanhove ◽  
Raquel Hermans ◽  
Tom Artois ◽  
Nikol Kmentová

Unlike their marine counterparts, tropical freshwater clupeids receive little scientific attention. However, they sustain important fisheries that may be of (inter)national commercial interest. Africa harbours over 20 freshwater clupeid species within Pellonulini. Recent research suggests their most abundant parasites are gill-infecting monogenean flatworms within Kapentagyrus. After inspecting specimens of 12 freshwater clupeids from West and Central Africa, mainly sourced in biodiversity collections, we propose 11 new species of Kapentagyrus which we describe using their haptoral and genital morphology. Because of their high morphological similarity, species delineation relies mostly on morphometrics of anchors and hooks. Specifically, earlier, molecular taxonomic work indicated that the proportion between the length of the anchor roots, and between hook and anchor length, are diagnostic. On average, about one species of Kapentagyrus exists per pellonuline species, although Pellonula leonensis harbours four species and Microthrissa congica two, while Microthrissa moeruensis and Potamothrissa acutirostris share a gill monogenean species. This study more than quadruples the number of known species of Kapentagyrus, also almost quadrupling the number of pellonuline species of which monogeneans are known. Since members of Kapentagyrus are informative about their hosts’ ecology, evolutionary history, and introduction routes, this enables a parasitological perspective on several data-poor African fisheries.


2021 ◽  
Author(s):  
Benedikt Ehrenfels ◽  
Julian Junker ◽  
Demmy Namutebi ◽  
Cameron M. Callbeck ◽  
Christian Dinkel ◽  
...  

Lake Tanganyika's pelagic fish sustain the second largest inland fishery in Africa and are under pressure from heavy fishing and global warming related increases in stratification. Only little is known about whether basin-scale hydrodynamics - including a more stratified north and an upwelling-driven south - lead to regional fish populations with varying ecological adaptations. Here, we examine whether the basin-scale dynamics leave distinct isotopic imprints in the pelagic fish of Lake Tanganyika, which may reveal differences in habitat, diet, or lipid content. We conducted two lake-wide campaigns during different seasons and collected physical, nutrient, chlorophyll, phytoplankton and zooplankton data. Additionally, we analyzed the pelagic fish - the clupeids Stolothrissa tanganicae, Limnothrissa miodon and four Lates species - for their isotopic and elemental carbon (C) and nitrogen (N) compositions. The δ13C values were significantly higher in the productive south after the upwelling/mixing period across all trophic levels, implying that the fish have regional foraging grounds, and thus record these latitudinal isotope gradients. However, the degree of regional isolation is insufficient to suppress lake-wide gene flow, suggesting that the fish form regional populations only on a basin-wide and seasonal scale. Based on δ15N and C:N ratios, we found no strong evidence for varying diets or lipid contents between those populations. Additional analyses revealed that isotopic variations between specimens from the same location are not linked to genetic differences. Our findings provide fundamental insight on the connectivity and ecology of Lake Tanganyika's pelagic fish and imply that sustainable management strategies may adopt basin-scale fishing quotas.


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