De Meester, N.

Derycke, S.

Moens, T.

De Meester, Nele

Derycke, Sofie

Moens, Tom

Ghent University Academic Bibliography

SAME LOOKS, DIFFERENT PREFERENCES: SALINITY EFFECTS ON THE COEXISTENCE OF CRYPTIC SPECIES. De Meester Nele1, Sofie Derycke1 and Tom Moens1 1  Marine Biology, Dept. Biology Ghent University, Krijgslaan 281/S8, 9000 Ghent  E-mail: nele.demeester@ugent.be   Behind the morphological similarity of many species, a substantial hidden genetic diversity can be found. This hidden or cryptic diversity leads to a significantly higher biodiversity in ecosystems than previously regarded and is important for estimating total diversity on earth. It has been well documented in the marine nematode, Rhabditis (Pellioditis) marina (Derycke et al., 2008), where several cryptic species occur sympatrically (Pm I, Pm II, Pm III and Pm IV). This coexistence challenges traditional ecological competition theory, stating that competition will be most severe between closely related species, rendering coexistence unlikely. Niche partitioning, where species coexistence is explained by differences in phenotype is a possible way to achieve such coexistence. Closely related sympatric species, despite only minor differences in morphology, can display different preferences for abiotic conditions. So if cryptic species differ in their response to ecological heterogeneities, their coexistence may be facilitated and the outcome of competition will depend on fluctuations in the abiotic environment. Studying these preferences and more broadly the ecology of cryptic species can lead to a better insight in the origin of cryptic speciation and the geographical distribution of these cryptic species.   Rhabditis (Pellioditis) marina is a common bacterivore associated with decomposing macro-algae in the littoral zone of coastal and estuarine environments. One of the possible factors shaping the distribution patterns and coexistence of the cryptic species is salinity, one of the most conspicuous environmental factors causing heterogeneity in tidal environments. The effect of salinity on the coexistence of cryptic species was studied in a lab experiment, where population structure between competition cultures (with equal abundances of four cryptic species together) and monospecific cultures (where the four cryptic species can not affect each other’s population development) was compared at two different salinities. The results showed an effect of competition and salinity on the population structure with (1) an increased time-averaged abundance of Pm III at the low salinity in monospecific cultures, (2) a negative effect of competition on the abundance of two cryptic species (Pm II and Pm IV) and (3) stronger competition at lower salinity. Lower salinity has mostly an intensifying effect on the outcome of the competitive interactions and besides competition, complete exclusion (Pm IV) and facilitative interactions occurred (Pm I and Pm III at high salinity). These results show that changes in the abiotic environment (in casu salinity) can shift the outcome of competition between and hence the possibility of the coexistence of different cryptic species of Rhabditis (Pellioditis) marina.       References   Derycke S., Fonseca G., Vierstraete  A., Vanfleteren J., Vincx  M. & Moens T. 2008. Disentangling taxonomy within the Rhabditis (Pellioditis) marina (Nematoda, Rhabditidae) species complex using molecular and morhological tools. Zoological journal of the Linnean Society 152: 1-15.    

English

Same looks, different preferences: salinity effects on the coexistence of cryptic species

Open Marine Archive

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SAME LOOKS, DIFFERENT PREFERENCES: SALINITY EFFECTS ON THE 
COEXISTENCE OF CRYPTIC SPECIES 
De Meester Nele, Sofie Derycke and Tom Moens 
Research Group Marine Biology, Biology Department, Ghent University, Krijgslaan 281, S8,  
9000 Ghent, Belgium 
E-mail: nele.demeester@ugent.be  
Behind the morphological similarity of many species, a substantial hidden genetic diversity can be 
found. This hidden or cryptic diversity leads to a significantly higher biodiversity in ecosystems than 
previously regarded and is important for estimating total diversity on earth. It has been well 
documented in the marine nematode, Rhabditis (Pellioditis) marina (Derycke et al., 2008), where 
several cryptic species occur sympatrically (Pm I, Pm II, Pm III and Pm IV). This coexistence 
challenges traditional ecological competition theory, stating that competition will be most severe 
between closely related species, rendering coexistence unlikely. Niche partitioning, where species 
coexistence is explained by differences in phenotype is a possible way to achieve such coexistence. 
Closely related sympatric species, despite only minor differences in morphology, can display 
different preferences for abiotic conditions. So if cryptic species differ in their response to 
ecological heterogeneities, their coexistence may be facilitated and the outcome of competition will 
depend on fluctuations in the abiotic environment. Studying these preferences and more broadly 
the ecology of cryptic species can lead to a better insight in the origin of cryptic speciation and the 
geographical distribution of these cryptic species.  
 
Rhabditis (Pellioditis) marina is a common bacterivore associated with decomposing macro-algae in 
the littoral zone of coastal and estuarine environments. One of the possible factors shaping the 
distribution patterns and coexistence of the cryptic species is salinity, one of the most conspicuous 
environmental factors causing heterogeneity in tidal environments. The effect of salinity on the 
coexistence of cryptic species was studied in a lab experiment, where population structure between 
competition cultures (with equal abundances of four cryptic species together) and monospecific 
cultures (where the four cryptic species cannot affect each other’s population development) was 
compared at two different salinities. The results showed an effect of competition and salinity on the 
population structure with (1) an increased time-averaged abundance of Pm III at the low salinity in 
monospecific cultures, (2) a negative effect of competition on the abundance of two cryptic species 
(Pm II and Pm IV) and (3) stronger competition at lower salinity. Lower salinity has mostly an 
intensifying effect on the outcome of the competitive interactions and besides competition, 
complete exclusion (Pm IV) and facilitative interactions occurred (Pm I and Pm III at high salinity). 
These results show that changes in the abiotic environment (in casu salinity) can shift the outcome 
of competition between and hence the possibility of the coexistence of different cryptic species of 
Rhabditis (Pellioditis) marina.  
 
References 
Derycke S., G. Fonseca, A. Vierstraete, J. Vanfleteren, M. Vincx and T. Moens. 2008. Disentangling 
taxonomy within the Rhabditis (Pellioditis) marina (Nematoda, Rhabditidae) species complex 
using molecular and morhological tools. Zoological journal of the Linnean Society 152:1-15. 


https://biblio.ugent.be/publication/2919707/file/2965920

Same looks, different preferences: salinity effects on the coexistence of cryptic species

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