Speciation in Obligately Plant-Associated Crematogaster Ants: Host Distribution Rather than Adaption Towards Specific Hosts Drives the Process
Ecological interactions among organisms may be an essential factor facilitating speciation processes. In one of the most species-rich ant–plant symbiotic systems worldwide pioneer trees of the euphorb genus Macaranga are inhabited by specific partner ants, mostly of the genus Crematogaster subgenus Decacrema. Both groups underwent radiation, with 30 species of Macaranga being colonized by eight species of Crematogaster. In this obligate association, the ants rely solely on their host for nutrition and nesting space. Hosts are distributed patchily in disturbed sites or gaps in primary forest. Association patterns are non-random in spite of the often sympatric occurrence of several host-plant species. Generally, each ant species colonizes two to seven different host species over its whole distributional range. Speciation processes in the ants may thus be driven either by adaptation towards alternative host species or by spatial patterns of host distribution, or by both factors. Limited dispersal of queens and nest site limitation due to the obligate association with a host were found to lead to significant isolation by distance on a small spatial scale in primary forest. Extremely high intraspecific genetic variation of mitochondrial markers was in contrast to the low genetic variability of nuclear markers, also pointing towards small population sizes of the ants and the importance of genetic drift in the diversification processes. Adaptation towards alternative hosts may occur as a by-product when different Macaranga hosts are colonized in different regions.
KeywordsHost Species Primary Forest Speciation Process Nest Space Founding Queen
We are very grateful to David Nash and two anonymous reviewers for comments on an earlier version of this manuscript. This work was supported by Deutsche Forschungsgemeinschaft (grants Ga661/2-1, Fe631/1-1, Fe631/1-2 and Fi606/5) within priority program SPP 1127 “Adaptive Radiations”. Permission to conduct research in Malaysia was kindly granted by the Economic Planning Unit (EPU) of the Prime Minister´s Office, Kuala Lumpur, and EPU in Kota Kinabalu, Sabah, as well as the Danum Valley Management Committee. Our permit to work in Brunei was obtained by Universiti Brunei Darussalam and Brunei Museum. We thank our counterparts and colleagues in Malaysia and Brunei for their cooperation and support, especially Prof. Datin Dr. Maryati Mohamed, Dr. Rosli bin Hashim, Dr. Kamariah Abu Salim, and members of Sabah Parks, namely Dr. Jamili Nais and Dr. Maklarin bin Lakim. Logistic support and help in many other ways by Prof. Dr. K. Eduard Linsenmair is gratefully acknowledged. We thank Prof. Dr. Ulrich Maschwitz for the kind supply of ant material. Barbara Feldmeyer, Sabine Frohschammer and Manfred Türke contributed greatly to field work. We are grateful for support in sampling and especially discussing speciation processes in this ant–plant association to Daniela Guicking, Frank Blattner, Kurt Weising, Ute Moog and Christina Baier from the accompanying Macaranga project.
- Davidson DW, McKey D (1993) The evolutionary ecology of symbiotic ant–plant relationships. J Hym Res 2:13–83Google Scholar
- Excoffier L, Laval G, Schneider S (2005) Arlequin ver. 3.0: An integrated software package for population genetics data analysis. Evol Bioinform Online 1:47–50Google Scholar
- Fiala B, Jakob A, Maschwitz U (1999) Diversity, evolutionary specialization and geographic distribution of a mutualistic ant–plant complex: Macaranga and Crematogaster in South East Asia. Biol J Linn Soc Lond 66:305–331Google Scholar
- Forel A (1910) Note sur quelques fourmis d’Afrique. Ann Soc Entomol Belg 54:421–458Google Scholar
- Forel A (1911) Fourmis de Bornéo, Singapore, Ceylan, etc. récoltées par MM. Haviland, Green, Winkler, Will, Hose, Roepke et Waldo. Rev Suisse Zool 19:23–62Google Scholar
- Maynard Smith J (1998) Evolutionary genetics. Oxford University Press, OxfordGoogle Scholar
- Moog U (2002) Die Reproduktion von Macaranga (Euphorbiaceae) in Südostasien: Bestäubung durch Thripse und Kastration durch Pflanzenameisen. PhD thesis, University of FrankfurtGoogle Scholar
- Swofford DL (2002) PAUP*: Phylogenetic analysis using parsimony. Ver. 4.0b10. Sinauer Associates, Sunderland, MAGoogle Scholar
- Weising K et al. (2010) Mechanisms of speciation in Southeast Asian ant-plants of the genus Macaranga (Euphorbicaceae) associated with Crematogaster ants. In: Glaubrecht M (ed) Evolution in Action. Springer, BerlinGoogle Scholar
- Yu DW, Davidson DW (1997) Experimental studies of species-specificity in Cecropia-ant relationships. Ecol Monogr 67:273–294Google Scholar