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Conserving our wildlife heritage: comparative biomechanics of feeding in native and introduced minks

Periodic Reporting for period 1 - MINKS (Conserving our wildlife heritage: comparative biomechanics of feeding in native and introduced minks)

Reporting period: 2019-09-02 to 2022-09-01

The European mink (Mustela lutreola) is currently considered the second most threatened mammal in Europe, with its main extinction risk being the American mink (Neovison vison). The invasive species is larger and less habitat-restricted than the native species and is an asymptomatic carrier of the Aleutian mink disease parvovirus (lethal to the European mink). Additionally, the American mink is an extremely competitive predator, which together with its larger size, allows it to overcome the native species in physical confrontations and even prey on it.
Conservation plans should focus on enhancing the survivability of the European mink and managing American mink populations. Feeding ecology provides a control checkpoint for both strategies. To date, it is unclear whether dietary overlap occurs between both mink species, although skull morphology would suggest that the American mink has access to a wider prey range. Knowledge of the biomechanics of feeding in both species is lacking.
MINKS investigates the biomechanics of feeding in minks to understand how morphological variation between European and American mink skulls influences the extent of dietary competition between both species.
To accomplish this, MINKS combines medical imaging and computer modelling techniques with methods for statistical shape analysis in 3D. Differences in skull shape between both mink species are first assessed, and then used to infer differences in the biomechanics of their feeding (that is, their function). This link between skull shape and its function allows the creation of theoretical dietary profiles, which simply put is all prey types that each species could eat based on biomechanical parameters of their feeding apparatus (how strong they bite, how wide their gape, etc.). When combined with studies on the diet of European and American minks in the wild, MINKS' findings will provide a deeper understanding of the success of the American mink over the native species. This new information can be used to enhance conservation strategies to ensure the survival of the European mink.
The results generated by MINKS depict a detailed scenario of dietary competition and niche segregation occurring between and within species. This theoretical scenario would have facilitated the prevalence of the invasive species over the native European mink, as male American mink are equipped to capture and process a larger range of prey and also come on top of aggressive inter- and intraspecific encounters. Conversely, the situation reverses for female European mink, which could mean that they are more frequently displaced from the food sources necessary to survive and rear their young. Thus, MINKS’ findings suggest that male American mink, due to their extremely wide dietary range and aggressive behavior towards other mink, particularly European mink females, should be the main target of any control strategies to reduce their numbers in the wild.
To fulfill the research aims, over 200 skulls of European and American mink were scanned using micro computed tomography and virtual 3D models of cranium and mandible were produced for each scan (freely available online). Cranium and mandible shape variation within and between both mink species was analyzed by identifying and digitizing sets of landmarks (Fig. 1) on those models and statistically comparing them.
MINKS’ main results, which have been published in 2 peer-reviewed articles so far (Journal of Anatomy, Scientific Reports) and presented in several international conferences, are summarized here:
- European mink crania do not present juvenile features relative to American mink
- American mink have relatively larger masticatory and neck muscles than European mink, but mandible shape adjusts muscle lever arms and mechanical advantage so that American mink are built for strong anterior bites (and thus killing small mammals) and European for fast mandible closure and strong cheek bites (ideal for feeding on aquatic prey) (Fig. 2)
- while increasing bite strength and gape require conflicting features, American mink can achieve both through compromises in skull shape
- as male mink get larger, their skull shape and biomechanics suggest that they specialize on eating terrestrial prey; while female mink shift from aquatic prey to terrestrial prey as they get larger
When combined, these findings create theoretical dietary profiles for both species and for males and females within them, profiles whose range is narrowest in European females and widest in American males. Comparing these profiles provides a deeper understanding of the success of the American mink over the native species by creating a scenario of dietary competition and niche segregation.
MINKS’ outputs represent the first comparison of skull shape between European and American mink and is one of the few 3D shape analyses that have been carried out in small mustelids. By using state-of-the-art techniques from multiple disciplines, MINKS has provided a deeper understanding of the success of the American mink over the native species based on its results on skull shape and feeding biomechanics and grounded in existing studies on mink diet in the wild and both hunting techniques and inter- and intraspecific interaction behaviors. MINKS’ findings will be useful in a number of research disciplines (e.g. conservation biology, paleontology, veterinary medicine, zooarchaeology). Additionally, the applied use of the data created by MINKS, particularly the processed 3D models, freely available on online repositories, is potentially limitless, since similar models of other species have been used in teaching, art (particularly life-like sculptures), publicity, and many more.
Note, however, that MINKS will continue to provide new data (e.g. 3D models of masticatory muscles) and results, as due to the covid-19 pandemic some of the acquired data has not been analyzed yet. The next step for MINKS will be visualizing and comparing muscle anatomy between and within species (Fig. 3), and beyond that engineering techniques such as Finite Element Analysis will be used to understand how the mink skull is built in order to resist the forces associated with prey capture and processing. All those studies will contribute to our knowledge of these species and provide an even deeper understanding of their ecology and interaction.

Besides MINKS expected outputs, a new diagnostic trait was described (the morphology of the pterygoid processes) that allows to visually identify between crania of European and American mink, and a set of landmarks allowing to statistically classify crania of an unknown mink species with a 100% correct classification rate was also defined. Both findings are particularly important for museum collections worldwide, as an alarming number of misclassified specimens were detected when acquiring MINKS’ sample.