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Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida).
Front Zool 2019; 16:24FZ

Abstract

Background

Mechanical defenses are very common and diverse in prey species, for example in oribatid mites. Here, the probably most complex form of morphological defense is known as ptychoidy, that enables the animals to completely retract the appendages into a secondary cavity and encapsulate themselves. The two groups of ptychoid mites constituting the Ptyctima, i.e. Euphthiracaroidea and Phthiracaroidea, have a hardened cuticle and are well protected against similar sized predators. Euphthiracaroidea additionally feature predator-repelling secretions. Since both taxa evolved within the glandulate group of Oribatida, the question remains why Phthiracaroidea lost this additional protection. In earlier predation bioassays, chemically disarmed specimens of Euphthiracaroidea were cracked by the staphylinid beetle Othius punctulatus, whereas equally sized specimens of Phthiracaroidea survived. We thus hypothesized that Phthiracaroidea can withstand significantly more force than Euphthiracaroidea and that the specific body form in each group is key in understanding the loss of chemical defense in Phthiracaroidea. To measure force resistance, we adapted the principle of machines applying compressive forces for very small animals and tested the two ptyctimous taxa as well as the soft-bodied mite Archegozetes longisetosus.

Results

Some Phthiracaroidea individuals sustained about 560,000 times their body weight. Their mean resistance was about three times higher, and their mean breaking point in relation to body weight nearly two times higher than Euphthiracaroidea individuals. The breaking point increased with body weight and differed significantly between the two taxa. Across taxa, the absolute force resistance increased sublinearly (with a 0.781 power term) with the animal's body weight. Force resistance of A. longisetosus was inferior in all tests (about half that of Euphthiracaroidea after accounting for body weight). As an important determinant of mechanical resistance in ptychoid mites, the individuals' cuticle thickness increased sublinearly with body diameter and body mass as well and did not differ significantly between the taxa.

Conclusion

We showed the feasibility of the force resistance measurement method, and our results were consistent with the hypothesis that Phthiracaroidea compensated its lack of chemical secretions by a heavier mechanical resistance based on a different body form and associated build-up of hemolymph pressure (defensive trade-off).

Authors+Show Affiliations

Department of Biology, Ecological Networks, Technische Universität Darmstadt, Schnittspahnstr. 3, 64287 Darmstadt, Germany.Department of Biology, Ecological Networks, Technische Universität Darmstadt, Schnittspahnstr. 3, 64287 Darmstadt, Germany.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31312228

Citation

Schmelzle, Sebastian, and Nico Blüthgen. "Under Pressure: Force Resistance Measurements in Box Mites (Actinotrichida, Oribatida)." Frontiers in Zoology, vol. 16, 2019, p. 24.
Schmelzle S, Blüthgen N. Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida). Front Zool. 2019;16:24.
Schmelzle, S., & Blüthgen, N. (2019). Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida). Frontiers in Zoology, 16, p. 24. doi:10.1186/s12983-019-0325-x.
Schmelzle S, Blüthgen N. Under Pressure: Force Resistance Measurements in Box Mites (Actinotrichida, Oribatida). Front Zool. 2019;16:24. PubMed PMID: 31312228.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Under pressure: force resistance measurements in box mites (Actinotrichida, Oribatida). AU - Schmelzle,Sebastian, AU - Blüthgen,Nico, Y1 - 2019/07/04/ PY - 2019/03/06/received PY - 2019/06/12/accepted PY - 2019/7/18/entrez PY - 2019/7/18/pubmed PY - 2019/7/18/medline KW - Euphthiracaroidea KW - Force measurements KW - Phthiracaroidea KW - Predator defense KW - Ptychoidy KW - Ptyctima SP - 24 EP - 24 JF - Frontiers in zoology JO - Front. Zool. VL - 16 N2 - Background: Mechanical defenses are very common and diverse in prey species, for example in oribatid mites. Here, the probably most complex form of morphological defense is known as ptychoidy, that enables the animals to completely retract the appendages into a secondary cavity and encapsulate themselves. The two groups of ptychoid mites constituting the Ptyctima, i.e. Euphthiracaroidea and Phthiracaroidea, have a hardened cuticle and are well protected against similar sized predators. Euphthiracaroidea additionally feature predator-repelling secretions. Since both taxa evolved within the glandulate group of Oribatida, the question remains why Phthiracaroidea lost this additional protection. In earlier predation bioassays, chemically disarmed specimens of Euphthiracaroidea were cracked by the staphylinid beetle Othius punctulatus, whereas equally sized specimens of Phthiracaroidea survived. We thus hypothesized that Phthiracaroidea can withstand significantly more force than Euphthiracaroidea and that the specific body form in each group is key in understanding the loss of chemical defense in Phthiracaroidea. To measure force resistance, we adapted the principle of machines applying compressive forces for very small animals and tested the two ptyctimous taxa as well as the soft-bodied mite Archegozetes longisetosus. Results: Some Phthiracaroidea individuals sustained about 560,000 times their body weight. Their mean resistance was about three times higher, and their mean breaking point in relation to body weight nearly two times higher than Euphthiracaroidea individuals. The breaking point increased with body weight and differed significantly between the two taxa. Across taxa, the absolute force resistance increased sublinearly (with a 0.781 power term) with the animal's body weight. Force resistance of A. longisetosus was inferior in all tests (about half that of Euphthiracaroidea after accounting for body weight). As an important determinant of mechanical resistance in ptychoid mites, the individuals' cuticle thickness increased sublinearly with body diameter and body mass as well and did not differ significantly between the taxa. Conclusion: We showed the feasibility of the force resistance measurement method, and our results were consistent with the hypothesis that Phthiracaroidea compensated its lack of chemical secretions by a heavier mechanical resistance based on a different body form and associated build-up of hemolymph pressure (defensive trade-off). SN - 1742-9994 UR - https://www.unboundmedicine.com/medline/citation/31312228/Under_pressure:_force_resistance_measurements_in_box_mites_(Actinotrichida,_Oribatida) L2 - https://frontiersinzoology.biomedcentral.com/articles/10.1186/s12983-019-0325-x DB - PRIME DP - Unbound Medicine ER -