TY - JOUR

T1 - Oil gland and oil pores in billfishes

T2 - in search of a function

AU - Dhellemmes, F.

AU - Hansen, M. J.

AU - Bouet, S. D.

AU - Videler, J. J.

AU - Domenici, P.

AU - Steffensen, J. F.

AU - Hildebrandt, T.

AU - Fritsch, G.

AU - Bach, P.

AU - Sabarros, P. S.

AU - Krüger, A.

AU - Kurvers, R. H. J. M.

AU - Krause, J.

PY - 2020

Y1 - 2020

N2 - © 2020. Published by The Company of Biologists Ltd. Billfishes are well known for their distinctive elongated rostra, i.e. bills. The functional significance of billfish rostra has been frequently discussed and the recent discovery of an oil gland (glandula oleofera) at the base of the rostrum in swordfish, Xiphias gladius, has added an interesting facet to this discussion regarding the potential co-evolution of gland and rostra. Here, we investigated the oil gland and oil pores (through which the oil is brought to the skin surface) of four billfish species - swordfish, Atlantic blue marlin (Makaira nigricans), Indo-Pacific sailfish (Istiophorus platypterus) and striped marlin (Kajikia audax) - and provide detailed evidence for the presence of an oil gland in the last three. All four species had a high density of oil pores on the forehead which is consistent with the hypothesis of hydrodynamic benefits of the oil. The extension of the pores onto the front half of the rostrum in sailfish and striped marlin, but not in swordfish or blue marlin, suggests that the oil may have additional functions. One such function could be linked to the antibacterial and anti-inflammatory properties of the oil. However, the available evidence on predatory rostrum use (and hence the likelihood of tissue damage) is only partly consistent with the extension of pores on rostra across species. We conclude that the oil gland probably serves multiple, non-mutually exclusive functions. More detailed information on rostrum use in blue marlin and swordfish is needed to better link behavioural and morphological data with the aim of accomplishing a full comparative analysis.

AB - © 2020. Published by The Company of Biologists Ltd. Billfishes are well known for their distinctive elongated rostra, i.e. bills. The functional significance of billfish rostra has been frequently discussed and the recent discovery of an oil gland (glandula oleofera) at the base of the rostrum in swordfish, Xiphias gladius, has added an interesting facet to this discussion regarding the potential co-evolution of gland and rostra. Here, we investigated the oil gland and oil pores (through which the oil is brought to the skin surface) of four billfish species - swordfish, Atlantic blue marlin (Makaira nigricans), Indo-Pacific sailfish (Istiophorus platypterus) and striped marlin (Kajikia audax) - and provide detailed evidence for the presence of an oil gland in the last three. All four species had a high density of oil pores on the forehead which is consistent with the hypothesis of hydrodynamic benefits of the oil. The extension of the pores onto the front half of the rostrum in sailfish and striped marlin, but not in swordfish or blue marlin, suggests that the oil may have additional functions. One such function could be linked to the antibacterial and anti-inflammatory properties of the oil. However, the available evidence on predatory rostrum use (and hence the likelihood of tissue damage) is only partly consistent with the extension of pores on rostra across species. We conclude that the oil gland probably serves multiple, non-mutually exclusive functions. More detailed information on rostrum use in blue marlin and swordfish is needed to better link behavioural and morphological data with the aim of accomplishing a full comparative analysis.

KW - Co-evolution

KW - Comparative method

KW - Fatty acids

KW - Functional morphology

KW - Glandula oleofera

KW - Rete lubricans

KW - Rostrum

U2 - 10.1242/jeb.224956

DO - 10.1242/jeb.224956

M3 - Journal article

C2 - 32796039

AN - SCOPUS:85092750627

VL - 223

JO - Journal of Experimental Biology

JF - Journal of Experimental Biology

SN - 0022-0949

M1 - jeb224956

ER -