Margaret K. Thayer.
Micralymma marinum (Stroem) in North America: biological notes and new distributional records (Coleoptera (Staphylinidae).
Psyche 92(1):49-55, 1985.

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MICRALYMMA MARINUM (STROEM) IN NORTH
AMERICA: BIOLOGICAL NOTES AND NEW
DISTRIBUTIONAL RECORDS
(COLEOPTERA: STAPHY LINIDAE)*
BY MARGARET K. THAYER
Museum of Comparative Zoology and
Department of Organismic and Evolutionary Biology Harvard University, Cambridge, Massachusetts 02138 Micral.vmma marinum (Stroem) is an amphi-Atlantic intertidal beetle whose wide distribution in the Old World is fairly well known (Lindroth 1931, 1957; Steel 1958), but its range in North America has not been well documented. LeConte (1863) described M. stirnp- sonii from the "coast of Maine." Lindroth (193 1:206) regarded this species as merely a variety of M. rnarinum and Steel (loc. cit.) listed it as a synonym of the latter. This synonymy has not been listed in North American catalogues (Leng et at. 1933-1948, Moore and Legner 1975) or Arnett's manual (1968). After comparing the uni- que type of M. stimpsonii (a female) with the North American specimens listed below, a specimen from Iceland identified by Lin- droth (also a female), and the illustrations (including aedeagus) pro- vided by Steel (1958), 1 agree that M. stimpsonii is synonymous with M. marinum. The vague type locality of M. stimpsonii, further south than any European records, has been the only record of the species from the United States, and although Lindroth (1957: fig. 32) mapped records from northwest, south, and southeast New- foundland and Steel (loc. cit.) mentioned seeing specimens from there, neither provided specific locality data. Since it appears that no specific New World locality records have been published for M. marinurn, it seems worth presenting some recently acquired data, particularly since one recent record extends the known range of the species south to Massachusetts at latitude 42O25'N. Two specimens collected by Palmkn whose records were apparently included on Lindroth's map (1957: fig. 32) are among those listed. Unless noted otherwise ("no ecol. data"), all of the specimens listed were collected on rocks or in rock crevices in the intertidal *Manuscript received by the editor October 2, 1984 49
Pu&e 92:49.55 (1985). hup Ytpsychu rinclub orgflMMM9 html



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50 Psyche [VOI. 92
zone (between high and low tide marks). The records are mapped in Figure 1. Specimens are in the collections of: American Museum of Natural History, New York [AMNH], California Academy of Sciences, San Francisco [CAS], Canadian National Collection, Bio- systematics Research Institute, Ottawa [CNC], Field Museum of Natural History, Chicago [FMNH], Paul J. Johnson, Moscow, Idaho [PJJ], Museum of Comparative Zoology, Harvard Univer- sity, Cambridge [M CZ], Memorial University of Newfoundland, St. John's [MUNF], University of New Hampshire, Durham [UNH], U. S. National Museum of Natural History, Washington [USNM], University Zoological Museum, Helsinki [ZMH], and the author and Alfred F. Newton, Jr., Cambridge [ANMT]. In the following records, A = adults and LI, LII, LIII = larvae of each instar. CANADA: NEWFOUNDLAND: Change Is., Aug. 1-9, 1981, lot 6, D. Larson [no ecol. data] (12A) [MUNF, ANMT]; Grand Bruit, S. Newfoundland, N:o 55, 18.6.1949, Ernst Palmkn [no ecol. data] (1A) [ZMH]; St. John Island, St. John Bay, NW Newfoundland, N:o 195, 3.8.1949, Ernst Palmh [no ecol. data] (1 A) [ZM HI; 2mi S St. Pauls, VIII-1-1972, J.M. Campbell (12A) [CNC, ANMT]; same locality, VIII-10-1972, J.M. & B.A. Campbell (15A) [CNC]. QUEBEC: Mont-St.-Pierre, VII- 18- 1972, J.M. Campbell (1 A) [CNC]. UNITED STATES: MAINE: Lincoln Co., Monhegan Island, nr. Seal Ledges, l6.VII. 1982, M. Thayer & A. Newton (374A; 312L: 16 LI, 108 LII, 188 LIII) [AMNH, ANMT, CAS, CNC, FMNH, MCZ, MUNF, PJJ, UNH, USNM, ZMH]; Monhegan I., N of Calves Cove, l7.VI I. 1972, M. Thayer & A. Newton (22A; 12L: 1 LI, 3 LII, 8 LIII) [ANMT]; Monhegan I., Deadman's Cove, 17.VII. 1982, M. Thayer & A. Newton (1 LII) [ANMT]; York Co., Isles of Shoals, Appledore Island, 28-29.V.1983, M. Thayer & A. Newton (25A, 4 L1I1) [ANMT, UNH]. MASSACHUSETTS: Essex Co., Nahant, nr. East Point, 10.VI11.1982, M. Thayer & A. Newton (2A) [ANMT, MCZ]. A further collection, undoubtedly of M. marinum although I have not seen the specimens, is: NEW HAMPSHIRE: Rockingham Co., Isles of Shoals, ne side of Star Island, 3 July 198 1, on intertidal rocks, W. F. Gimpel, Jr., collector (W. F. Gimpel, Jr., personal communi- cation).
There has been speculation about the natural food of M. mari- num, but no field observations have been made. Laboulbkne (1 858)



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Thayer - Micralymma 51
Fig. 1 .
Distribution of M. murinuni in North America. Circles represent records given in text; triangle represents a record mapped by 1-indroth (1957). exact locality unknown.
mentioned finding with M. rnarinurn abundant "Podurelles" (prob- ably Anurida maritima (Gukrin)), less abundant mites, and annelids and "petits coquillages." It is not clear whether the last refers to mussels, periwinkles, barnacles, amphipods, or something else. West (1930) said that M. rnarinurn are ". . .considered probably to prey on Thysanura," but Lindroth (193 1) regarded this claim (with- out giving any reference for it) as very unlikely because Thysanura are not known to occur at the Iceland M. marinum localities. Steel (1958, 1970) stated without giving reasons that "their main food appears to be the Collembolan Anurida maritima (Gukrin)" (Podu- ridae or Hypogastruridae). In my collecting 1 saw very few of these Collembola, some small mites, many barnacles, and many small and



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5 2 Psyche [vo~. 92
large amphipods in the areas where M. marinum was common. All except barnacles seem likely as potential food for the beetles. Beetles (both adults and larvae) that 1 kept in culture fed avidly on freshly- killed adult Drosophila spp., and were apparently still healthy after up to three and one-half months of such a diet. One third-instar larva finished its larval development feeding on these flies and pupated successfully. Clearly Micralyrnma marinurn are predators, but not obligate feeders on any element of their natural habitat; their usual natural food remains uncertain. King et al. (1979) suggested on the basis of collecting in southern Wales (at ca. 51å¡30'N that M, rnarinum overwinter as eggs or as adults, hidden deep in rock crevices. Steel (1970) suggested on the basis of his collecting in southwestern England (at ca. 50å¡43'N and in Scotland (at ca. 57'00'N) that adults overwinter and then lay eggs in May and June. One of the third-instar larvae I collected in Maine (at ca. 43'03'N) in late May pupated on 2 July and when preserved on 15 July appeared to be only a few days from adult eclosion. It appears from the last that in Maine some of the beetles may over- winter as larvae, or that the life cycle may be longer than one year. Steel (1970) found that most British Omaliinae overwinter as larvae (Thayer 1985 found the same for the North American species Brathinus nitidus LeConte and Lesteva pallipes LeConte), but M. marinum certainly occurs in a different habitat from most Omalii- nae and is undoubtedly subjected to different selective pressures. It is possible that the life cycle varies somewhat in different parts of the species' range.
With two exceptions, the morphological features discussed by King et al. (1979) and Elliott et al. (1983) in relation to the habitat of Micralymma marinum are all normal features of most or all Oma- liinae. The aptery of M. rnarinurn is unusual, though certainly not unique, within the subfamily. Its connection with the habits of the species is open to question, however, since the other species in the genus (M. brevilingue SchiMte, M. caucasicum (Melichar)) are also apterous (Steel 1958, 1962) and M. marinum is the only one that is stricly marine intertidal (Steel 1962). Of perhaps more interest is the modification of the tarsal setae mentioned by both King et al. (loc. cit.) and Elliott et al. (loc. cit.). Micralymma marinum has, as they pointed out, flattened and widened ventral tarsal setae on the first four segments of all tarsi in both sexes. They are slightly more



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19851 Thayer - Micralymma 53
strongly modified in males than females, and those on the male pro- tarsi are more distinctly flattened than those on the other tarsi. Most species of Omaliinae, if possessing flattened tarsal setae at all, have them only on the protarsi (sometimes also mesotarsi) of males (Thayer and Newton 1979; author's unpublished data), presumably aiding in grasping females during mating. The distribution of the specialized setae in M. marinum is very much like that found in omaliine genera whose adults are flower-inhabiting pollen feeders (Eusphalerum, Pelecomalium, Amphichroum, Austrolophrum, and Anthobiomimus). In both cases it seems to be an adaptation facili- tating adhesion to the exposed surfaces on which the beetles occur (see Stork 1980, 1983), with the more pronounced development in males again presumably related to adhesion to females during mating.
King et al. (loc. cit.) mentioned the pupa of M. marinum as having "a number of long lateral setae . . . which presumably also help in maintaining position" in rock crevices. These long projec- tions (not actually setae) are found in all described omaliine pupae (Olophrum, Paulian 194 1 ; Antarctotachinus, Jeanne1 1940; Brathi- nus, Thayer 1985) and Microedus (author's unpublished data). Of these, all but Brathinus have pairs of similar projections parame- dially on the abdominal tergites as well. (Laboulbbne 1858 illus- trated the pupa of M. marinum but apparently overlooked the dorsal projections.)
Lindroth (1 93 1, 1957) proposed that Micralymma marinum orig- inated in North America and that its trans-Atlantic distribution resulted largely through passive transport of beetles by the Gulf- stream, attached to pieces of seaweed, driftwood, or other flotsam. This explanation does seem ecologically, physiologically, and meteorologically plausible (Laboulbkne 1858 and Elliott el al. 1983, immersion tolerance data; Lindroth 1931 and 1957, map of Gulf- stream), but another factor that must be considered in analyzing the historical biogeography of the species is its phylogenetic relation- ship to the other species of the genus: where might the common ancestor of M. marinum and its sister-species (or sister-group) have occurred? As this phylogenetic question has not yet been explored, the question of why Micralymma marinum is where it is must be regarded as only tentatively answered.




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34 Psyche [Vol. 92
This research was done largely during the tenure of a NSF Grad- uate Fellowship. I thank P. S. Thayer for accommodations on Monhegan Island, the Edwards Marine Science Institute of North- eastern University for access to the Nahant collecting site, and A. Borror (Shoals Marine Laboratory) for his hospitality and for permission to collect on Appledore Island. My thanks also go to J. M. Campbell (Biosystematics Research Institute, Ottawa) for the loan of CNC specimens of Micralymma; D. Larson (Memorial Uni- versity of Newfoundland, St. John's) for his gift of specimens; H. Silfverberg (University Zoological Museum, Helsinki) for the local- ity information from Palmen's specimens; M. Huybensz for arrang- ing the trip to Appledore and him and M. Ormes for assistance in the field there; W. F. Gimpel, Jr. (Maryland Department of Agricul- ture, Annapolis) for information on the specimens he collected on Star Island; and P. J. Johnson (formerly MCZ-Harvard Univer- sity, now University of Idaho, Moscow) for reading and offering helpful comments on the manuscript. Special thanks are due A. I?. Newton (MCZ-Harvard University) for his enthusiastic help in collecting Micralymma as well as for reading and commenting on the manuscript.
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