Optimal species distinction by discriminant analysis: comparing established methods of character selection with a combination procedure using ant morphometrics as a case study

Global change may make hostile - Higher ambient temperature and nitrogen availability increase ant aggression

Behaviour is a response of organisms to internal and external stimuli and comprises various activities such as searching for food. Aggression is important in such activities, for example, improving the chances of winning competition for food, but animals differ in their level of aggression. This behavioural plasticity allows individuals to respond to environmental changes and is important for the survival of animals. It may be an important asset in facing global changes, which affect all organisms, for example, via rising temperature and eutrophication. The latter have steadily increased since 1900, especially in high elevations. Their effects may first become visible in stationary organisms such as ants because their nests are strictly associated with the conditions on site. Here, we analysed eight populations of the high-elevation ant Tetramorium alpestre along several elevations spanning the European Alps. We conducted a correlative approach and analysed several genetic and environmental proxies, namely within- and across-colony genetic relatedness, cuticular hydrocarbons, body size, across-colony geographic distance, air temperature, and worker nitrogen values additionally to within-population aggressive behaviour. We hypothesised that a) these proxies and aggressive behaviour differ among populations and that b) one or more of these proxies influence aggression. We found that a) some environmental proxies and aggression differed among populations but not the genetic proxies and that b) air temperature and worker nitrogen-isotope values correlated positively with worker aggression. The results indicate an environmental but not social-structural influence on this ant's aggressive behaviour, even though social structure varied among populations (single- and multiple-queened colonies). We infer that global change affects aggression in our study system and propose five mutually non-exclusive scenarios to explain the behavioural change mechanistically. Using the space-for-time principle, we speculate that aggression may increase due to future increases in temperature and nitrogen availability in this ant and other species living in high elevations.

Taxonomist's Nightmare … Evolutionist's Delight : An Integrative Approach Resolves Species Limits in Jumping Bristletails Despite Widespread Hybridization and Parthenogenesis

Accurate species delimitation is fundamental to biology. Traditionally, species were delimited based on morphological characters, sometimes leading to taxonomic uncertainty in morphologically conserved taxa. Recently, multiple taxonomically challenging cases have benefited from integrative taxonomy-an approach that highlights congruence among different disciplines and invokes evolutionary explanations for incongruence, acknowledging that different methods can mirror different stages of the speciation continuum. Here, we used a cohesive protocol for integrative taxonomy to revise species limits in 20 nominal species and 4 morphospecies of an ancestrally wingless insect group, the jumping bristletail genus Machilis from the European Eastern Alps. Even though morphologically conserved, several small-scale endemic species have been described from the Eastern Alps based on variation in hypodermal pigmentation patterns-a highly questionable character. As valuable as these endemics are for conservation, they have never been verified by alternative methods. Using traditional morphometrics, mitochondrial DNA, ribosomal DNA, and amplified fragment-length polymorphism markers, we identify six nominal species as taxonomic junior synonyms (Machilis alpicola Janetschek, 1953 syn. n. under M. vagans Wygodzinsky, 1941; M. ladensis Janetschek, 1950 syn. n., M. robusta Wygodzinsky, 1941 syn. n., and M. vicina Wygodzinsky, 1941 syn. n. under M. inermis Wygodzinsky, 1941; M. aleamaculata Wygodzinsky, 1941 syn. n. under M. montana Wygodzinsky, 1941; M. pulchra Janetschek, 1950 syn. n. under M. helleri Verhoeff, 1910) and describe two new species (Machilis cryptoglacialis sp. n. and Machilis albida sp. n.), one uncovered from morphological crypsis and one never sampled before. Building on numerous cases of incongruence among data sources, we further shed light on complex evolutionary histories including hybrid speciation, historical and recent hybridization, and ongoing speciation. We hypothesize that an inherent affinity to hybridization, combined with parallel switches to parthenogenesis and repeated postglacial colonization events may have boosted endemicity in Eastern Alpine Machilis We thus emphasize the importance of integrative taxonomy for rigorous species delimitation and its implication for evolutionary research and conservation in taxonomically challenging taxa.

Integrative taxonomy: a multisource approach to exploring biodiversity

Good alpha taxonomy is central to biology. On the basis of a survey of arthropod studies that used multiple disciplines for species delimitation, we evaluated the performance of single disciplines. All included disciplines had a considerable failure rate. Rigor in species delimitation can thus be increased when several disciplines chosen for complementarity are used. We present a flexible procedure and stopping rule for integrative taxonomy that uses the information from different disciplines separately. Disagreement among disciplines over the number and demarcation of species is resolved by elucidating and invoking evolutionary explanations for disagreement. With the identification of further promising study organisms and of new questions for in-depth analysis, evolutionary biology should profit from integrative taxonomy. An important rationale is clarity in researcher bias in the decision-making process. The success of integrative taxonomy will further increase through methodological progress, taxonomic training of evolutionary biologists, and balanced resource allocation.