Experimental Interbreeding Between Geographically

Marine Biology 17, t49--157 (1972) by Springer-Verlag t972

Experimental Interbreeding between Geographically Separated Populations of the Marine Wood-Boring Isopod Limnoria tripunctata with Preliminary Indications of Hybrid Vigor*

R. J. Menzies

Oceanography Department, Florida State University; Tallahassee, Florida, USA

Abstract larval stage, and are restricted by food requirements Populations of the marine wood-boring isopod Limnoria and habitat preference to submerged wood in the sea. tripunctata Menzies were cultivated and interbred in the Each piece of infested wood supports a more or less laboratory in order to determine whether geographically unique population. Within a restricted migratory or separated populations would interbreed. Two series of inter- swimming range, gene-flow is ]probably continuous and breeding studies were conducted. In the first, field populations from li Atlantic and Caribbean sites and 3 Pacific sites were a population in a given harbor or bay may be consid- interbred with a North Western Atlantic population from ered to constitute one "deme". Beaufort, North Carolina (USA). Viable crossings, to at least Between harbors, the amotmt of submerged wood F1, occurred in all but one case -- that of a Beaufort • Chat- available is usually slight, most having found its way ham (Massachusetts, USA) cross. In the second series of experiments, field populations from 9 Atlantic and Caribbean to the shore-line where silt, sand, and desiccation make sites were crossed with populations from St. Teresa, Florida, it unfit for Limnoria tripunctata. It was believed that Gulf of Mexico. In this ease also, all crosses except one pro- the crossing of populations from different harbors duced viable offspring, not only to the 2'I, but to the F~ gene- should yield some interesting information on the com- rations as well. The St. Teresa • Chatham cross was not successful. Geographic distance was not a factor in the success putability of geographically disjunct populations of of crossbreeding between disjunct populations. Chatham popu- the same species. Presumably gene-flow should be lations (mainly) are now believed t~) represent a valid but greatest (even though low, at best) between geograph- previously obscure species, Limnoria tuberculata Sowinski, ically close harbors, and least between more distant and not a variant of L. tripunctata Menzies. Enhanced vitality or vigor, as determined from rate of wood destruction, popu- harbors. lation growth rate and survival, was indicated in several crossings, but this was not necessarily correlated with distance Geographic Distribution between populations. Observations were made on the manner in which the species has achieved a worldwide distribution, and Limnoria tripunctata Menzies has a worldwide a hypothesis is put forward to explain the evolution of species distribution in the tropical, subtropical, and partly related to L. tripunctata. temperate seas. It has been collected between Boston, Massachusetts and Bahia Blanca, Argentina, in the Introduction Western Atlantic Ocean, including the Gulf of Mexico and Caribbean Sea, and between Plymouth, England The problem was to determine whether geograph- and Dakar, Senegal in the Eastern Atlantic Ocean, ically isolated populations of the marine isopod as well as the Mediterranean and Red Seas. In the Limnoria tripunctata were reproductively compatible. Pacific Ocean, it is distributed between San Francisco In major microscopic characteristics they had already Bay and Balboa, Panama, and among the islands of been determined to be phenotypica]ly conspecifie the Western and Central Pacific Ocean from Japan (Menzies, i957). This problem involves a number of to Northern Australia. In the Indian Ocean it has been sub-problems concerning the experimental methods recorded from Madras and Mombassa. This distribu- required for successful cultivation of marine species tion is a close parallel to subtropical-tropical tempera- from geographically distant localities. tm'e ranges (Menzies, 1959). The isopods are dioecious, lack a free swimming The contacts Limnoria tripunctata Menzies makes * Contribution from Zoology Department, Duke Universi- with other species at its northern range are of some ty, Durham, North Carolina, and Duke University Marine interest. On the Pacific coast, it meets Zimnoria Laboratory, Beaufort, North Carolina, and the Department of Oceanography, No. 289, Florida State University, Tal- quadripunctata Holthuis at San Francisco Bay, Cali- lahassee, Florida. Support in part from NSF Grant l~o. GB- fornia, where it is found sympatrically with that species 6898. (Menzies, 1958). North of Point Arenas, California, 20 MarineBiology, Vol. 17 t50 R.J. Menzies: Experimental Interbreeding in Limnoria Mar. Biol.

L. quadripunctata is replaced by Limnoria lignorum conditions in order to reach compatible thermal con- Rathke. A similar situation occurs in England, but ditions. there all three species are found together (Jones, 1963). The two southern species are replaced in Nor- Reproduction and Temperature way by L. lignorum Rathke. On the Atlantic coast of The relationship between reproduction and tem- North America, L. tripunctata meets L. lignorum at perature is a strong one in Limnoria tripunctata, and Chatham, Massachusetts. On this coast, however, appears to be related to the duration of temperature L. quadripunctata is absent. Kussakin (1963) has des- favorable for reproduction throughout the year. cribed species of Limnoria from the low Arctic. It Beckman and Menzies (i960) found that the species seems likely that his Arctic "species" are closely re- would breed and reproduce under laboratory condi- lated to L. lignorum. This contention might be subject tions between 15~ and 30 ~ This range of temperature to simple testing through interbreeding experiments coincides almost exactly with the temperature range such as those reported here. How a pantropical distri- encountered by the species in nature. The optimal bution has been realized in L. tripunctata has not yet temperature, at which reproduction rate was highest, been determined. It is commonly believed that the was between 20 ~ and 25 ~ Although the correlation isopods were transported on the infested hulls of between distribuSion and a temperature range of wooden ships and, although not the orrly one, that i5 ~ to 30 ~ is great, a better correlation is established seems a possibility. The chances are equally good that between the duration of temperatures favorable for the species had a worldwide thermal distribution reproduction and distribution. during the Eocene, and is now restricted to the modern limits of the subtropics and tropics. Although the possibility of occasional introductions Mode of Reproduction into a given locality from elsewhere must be admitted, it is reasonable to believe that the closer one location Limnoria, like many other marine isopods, is dioe- is to another, the better the chance of gene inter- cious, and requires the presence of a male and a female change. It has been demonstrated that populations for successful reproduction. Transfer of sperm to the of Limnoria tripunctata (Menzies, 1968) can withstand female has not been observed due to the secretive transit through the fresh water of the Panama Canal, nature of the animals. The male sexual apparatus and in the days of wooden ships, such transport might consists of a pair of genital apophyses located on the have been one mode of dispersal. By the time She canal midline at the caudal end of the seventh peraeonal was built, however, wooden ships were not in wide use. (thoracic) somite (Fig. t B). Sperm transfer is assisted The possibility of transisthmian transport of specimens by the appendix masculinum attached to the inner in the ballast tanks of ships cannot be excluded, but margin of the endopodite of the second male pleopod. iS is a remote possibility due to the foul conditions usually found in ship ballast and bilges. Transport of driftwood around Cape Horn and the Cape of Good Phenomena Associated with Reproduction Hope from one ocean to another would be difficult. On old infested wood, gravid females are usually Infested pieces of wood would have to originate in the found in the blind end of a burrow, with the male near tropics or subtropics and enter boreal and antiboreal the entrance (Fig. 2). Usually new burrows are started

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Fig. ~. Limnoria tripunctata. Sections showing'reproductiveapparatus. (A) Female; (B) male Vol. 17, No. 2, 1972 R. J. Menzies: Experimental Interbreeding irt Limnoria 151

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Fig. 2. Limnoria tripunctata. Section of infested wood showing position of male, female, and larva

by the male. The female enters a newly started burrow Experimental Design as soon as it is long enough and large enough for All of the foregoing characteristics of reproduction double occupancy. The female enters a burrow in a and ecology have a bearing on the desigaa of the pregravid state, in which the oSstegites are small experiments. The most significant variable, ff ecologic and the internal ova are ripe for fertilization. Copula- factors remain favorable, is the reproductive behavior tion occurs in the burrow and is apparently simul- of the species. Limnoria tr@unctata lacks any sperm r with a moulting of the female because, at this storage mechanism, hence pairing of a male with a time, ~he large o6stegites are produced, the huge eggs "virgin" female is a prerequisite to successful repro- pass through the oviducts, are fertilized during passage duction. It is essential that females obtained from and are deposited in the marsnpium produced by the nature are not carrying "wild-type" spermatozoa large o5stegites (Fig. t A). At this time the male and from previous fertilizations and that the male, which female reverse their positions in the burrow. is given to her in the laboratory, is the donor of sperm E]tringham and Hockley (1961) correctly pointed and father of the fLrst brood. out that the change in burorw position is related to With other species of isopods, this approach could reproduction activities. The switch places the female not be used due to the presence of a seminal receptacle with her eggs and young in the most protected situa- in which sperm are stored from one brood to the next, tion leaving the males most vulnerable to attack by as in the Asellota and Sphaeromidae (~enzies, t954), predators. or due to the parthenogenetic production of young as After incubation, the young emerge from the marsu- in certain Oniscoidea. plum and commence feeding immediately. The female then undergoes a moult which restores her o6stegites Taxonomy to pregravid size. She now can swim well and often Limnoria tripun~tata Menzies (t95i) is most closely abandons her burrowing young in a migratory mamler. related to L. tuberculata Sowinski from the Crimea, Southern England (personal observation) and from Chatham, Massachusetts (personal observation). Addi- Other Facets o] Ecology tionally, it shows some obvious points of similarity The effect of temperature on Limnoria tripunctata with the deep-water species L. japonica Richardson, has been alluded to above. Temperature influences and with L. saseboensis Menzies from Sasebo, Japan the reproduction and growth rate and, as a conse- (Menzies, t957). Because closely related known species quence, determines the geographic distribution of the occur at or near the coldest temperature range of the species. species, it is suggested that natural selection related In addition, salinity has a marked effect oll Lim- to cold temperature requirements may be a major noria (Eltringham, ~t961a). The isopod ~olerates salini- factor in ]~he evolution of certain species in ~his genus. ties between ~2 and 48 ~o. Boring ceases and starvation It is rather easy to visualize a continuous selection occurs at sallnities below t0 Yoo. The oxygen consump- pressure towards cold adaptation in populations of tion of Limnoria is reported as 1853 [zl/g (dry weight) L. tripunctata residing at the fringe of their thermal at 25 ~ and 1253 91 at 20 ~ by Eltringham (i965). survival, with a gradual selection of genofypes which Limnoria can tolerate low oxygen concentrations in are able to withstand colder climates. In the case of nature. Specimens were found in water ranging as low L. tuberculata, the morphologic expression of a few as i part per million dissolved oxygen (Menzies et al., added tubercles on the pleofe]son appears to have 1963), and in experiments the animals tolerated accompanied the cold adaptation..L, tuberculata So- oxygen tensions as low as 3 to 4 % saturation (Eltring- winski was recently, but incorrectly, made a senior ham, i96tb). synonym of L. tripunctata by Esakova (1965). 20* i52 R.J. Menzies: Experimental Interbreeding in Limnoria .Mar. Biol.

Methods Cultivation Temperature One of the most crucial aspects of the experimental Each experimental group of isopods was kept in procedures invoIves the selection of uninjured speci- its culture dish in a BOD box which was set at 23 ~ mens for experimental purposes. After a piece of This is the optimum temperature for population infested wood is collected from the field, the problem growth as determined by Beckman and Menzies remains to extract the isopods without injury. The (~960). Filtered seawater, obtained from the habitat procedure employed in these experiments consisted of of the control populations, was changed weekly at cutting the wood into thin slices, thus exposing the each count of fecal pellets, when a check was made to burrows and recovering only those individuals which assure that the salinity had not fallen below 20%0. swim. The isopods were removed with a pipette once they were seen swimming. The swimming specimens included all size classes except the recently emerged Establishment of Cultures young, the gravid females and the injured specimens Ten male Limnoria tr~punctata were introduced which were too inactive to swim. Two hundred or more into the culture dish. At first they remained on the viable isopods were collected in this way, placed in a bottom of the dish, but usually all had found the 12" (30 cm) finger bowl half full of seawater, and pro- floating piece of wood by the end of I day. Each day, vided with paper toweling or filterpaper to which they any dead or injured specimens were removed and re- could cling and feed. placed with active males. By the end of ~ month, Each day dead individuals (probably injured as a i0 males had each constrneted burrows of sufficient consequence of slicing the wood) were removed. Speci- length to permit introduction of the females. In addi- mens are easily activated with a stream of seawater tion, other burrows had been started and abandoned. from a pipette, and were removed for determination of sex and age. The procedure for sex determination is also critical, because the animals must be somewhat Introduction of Females immobilized and viewed ventrally. Each specimen was As soon as the burrows of the males were completed, placed on a microscope slide, in a drop of water small the ~[0 virgin females were added. Usually by the end enough to restrict its swimming and coiling. It was of I day, each female had found a burrow and was then examined with a binocular microscope at l0 to occupying it with a male. 50 times magnification. Isopods with their ventral sides up could then be sexed. Those with the dorsal side up were examined by inverting the microscope Results and Co-cluslons slide over a hole in a match box. Thus, the animals The results are described with reference to two were not touched or injured during the examination. distinctly separate series of experiments, each with Sexes were determined by the presence or absence of slightly different objectives. genital apophyses and oSstegites. Gravid females were not used. Intersexes were encountered with such rarity that they were not taken into account in the Series "X" selection of specimens (Menzies, 1954). Sexed indi- This series of experiments attempted to determine viduals, usually found in a 50:50 ratio, were placed whether it was possible to interbreed geographically separately in small culture dishes with filtered sea- disjunct populations of Limnoria tripunctata. Field water and a piece of Whatman No. 00 filter paper to populations from II localities along the Atlantic and provide a substratum for these thigmotropic animals. Pacific Coast (Table l) were placed with resident When required, cultures were disturbed with a stream of water and only active swimming specimens were selected for use in the culture experiments. Table 1. Percentage o/ adult and young (t'1) /ecal pellets produced by (A) control crossing of Limnoria tripunctata /rein Chatham; (B) attempted crossing el L. tripunctata • Preparation of Culture and Food Supply L. tuberculata between Chatham and Beau/oft

Culture dishes of l0 cm diameter and l0 cm height Date examined A B were filled with filtered seawater. A block of wood which Adult Young Adult Young had previously been soaked in seawater for 2 weeks was placed in each dish. At first, the block of wood (Douglas fir or pine) floated, but later became so 5. X. 1966 65 35 91 9 water-logged that it sank to the bottom. In order 22. XI. t966 81 19 99.7 0.3 17. XII. J966 78 22 t00 0 to keep the wooden block at the surface, and hence 16. I. 1966 75 25 100 0 facilitate gas exchanges, a string was tied to it and 8. V. i967 63 37 100 0 attached to the lid of the culture dish. Vot. 17, No. 2, 1972 R. ft. Menzies: Experimental Interbreeding in IAmnoria i53

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1,4 8 t54 R.J. Y[enzies: Experimental Interbreeding in Limnoria .Mar. Biol. populations from Beaufort, RTorth Carolina. Successful the experimental cross exceeded that of the control, a interbreeding established the utility of the cultivation vigor of one ( + ) was assigned to the crossing. Similar- methods, and permitted the examination of other ly, when the experimental cross produced young in questions in the Series "Y" experiments. For instance, fewer days than the control another + value was added in Series "X", no attempt was made to prevent the The assignment of these values permitted an expression P1 • F1 backeross, nor was any attempt made to of cross-culture vigor relative to that of the control. determine population growth by sacrificing cultures. Data for hybrid vigor are given in Table 2. They It was considered more important at tiffs stage to suggest that populations within 1,000 km distance of demonstrate successful cultivation and successful the control site may or may not show unusual vigor, Pc • Px interbreeding, where Pc is an adult from the while those 2,000 km distance and greater do not. resident control population in Beaufort and Px is an Although the results of the Series "X" experiments adult of opposite sex from some distant locality. were not conclusive, they were considered of sufficient In the Series "X" experiments, the diameter of the interest as preliminary indicators to justify another fecal pellet was used as an index of production of series in which other criteria were added to unify young. Fecal pellets in Limnoria tr@unctata consist of hybrid vigor. macerated wood compacted into microscopic logs. The diameter of these logs is an index of the diameter Series "Y" Experiments of the gut of the individual which produced them. The procedure for the establishment of cross As soon as the females were added and the pairing cultures was the same as that for the "X" experiments. commenced, a weekly record was kept of the propor- The source of control cultures was Saint Teresa, tion of adult and young fecal pellets. Each test block Florida instead of Beaufort, North Carolina. At the was washed with seawater to remove clumps of feces appearance of F~ young, the adults of the P~ genera- adhering to the entrance (Fig. 2), and the washings tion were sacrificed. Any F 2 generation produced was, settled out at the bottom of the dish. After stirring therefore, the result of an _~ • E 1 cross, and not a the water to mix thoroughly all size classes of fecal back cross of P~ • F~ as was possible in the "X" pellets, an aliquot was recovered and the diameter of series. The results are shown in Table 3 and Fig. 3, i00 fecal pellets measured. The first appearance of where each cross is indicated. Some comment is re- small-diameter fecal pellets in the culture dish was quired on each column of these data. taken as evidence of the appearance of the F~ generation. Changes in the mean diameter of fecal pellets F 1 Produced recovered from the crossing constituted a measure of An F1 generation was produced ( + ) in each of the individual growth. 12 experiments and the 4 controls. The appearance This technique allowed the indirect measurement of the F 1 was determined by observing the presence of individual and population growth. Direct measure- of minute fecal pellets produced by emergent young ment would have necessitated the destruction of the of the/~z generation. burrows. The results of the "X" experiments (Tables I and 2) show that it was possible to interbreed geographi- Average Days to F 1 cally disjunct populations under laboratory conditions, The days required for the successful production of with the exception that the Chatham • Beaufort cross an F 1 generation after introduction of the females failed to produce viable young. The failure of young showed considerable variation, from 28 days for production by the Los Angeles • Beatffort cross was Balboa, Canal Zone to ii9 days for Savannah, Georgia due to an accidental apparatus breakdown rather than and Charleston, South Carolina. Apparently this a failure to reproduce. The cause of the Chatham • variation is closely correlated with season of collection Beaufort reproductive failure required further in- and a seasonality of reproduction, as suggested by vestigation. The record is especially interesting in that Beckman and Menzies (1960). All cultures, controls an -~1 was produced by the cross, but it died shortly included, were started between November and January after being produced. This is shown by the abundance except the Balboa and Coco Solo series which were of F1 young fecal pellets in comparison with the started in April. The rapid reproductive response of adults (Table i). the Chatham • St. Teresa cross is inexplicable, unless Hybrid Vigor it is attributed to some curious speed-up of the deve- lopment of hydrid young having lethal genes. None Hybrid vigor was measured in the Series "X" of the young produced in this cross survived. experiments on the basis of two observations; the time required to achieve an F 1 generation after females were introduced into the culture, and the proportion 2' 3 Produced of "young" feces produced in the F 1 compared with An F~ generation was produced by the F 1 • F 1 the control. When the per cent of young F 1 feces by cross in all instances except the Chatham x St. Teresa Vol. 17, No. 2, 1972 R.J. l~enzies: Experimental Interbreeding in Limnoria 155

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SAME AS DIFFERENT FROM CONTROLO CONTROL

StTeresa CONTROL 3hatharn Sovonnoh 0 Charleston 0 Norfolk IOI Coco Solo HH 3alboa LosAngetes O San Francisco O 3alveston =. l Wilmington I ". l Beoufort San d,tan 0 50 I00 150 200 F-2 pOPULATION GROWTH "Y"SERIES

Fig. 3. Limnoria tripunctata. Population growth of crossings with field populations from various locations in the USA

cross. These data tend to support the results of the between 0.83 and 2.15 ml feces/culture/day. Under the Series "X" experiments. constant laboratory conditions, this rate should be constant per individual or at least equal to the control Average Days to _~ rate/individual. It is not constant, as may be seen below. Accordingly, the data suggest that individuals of The number of days between the first appearance the F 1 generation were identical with the control in of an F 1 generation and the firs~ appearance of the feeding rate (young produced plus growth) only in the F~ generation is a measure of the generation time for cases of populations from Savannah, Georgia. The this species under control conditions. The range was data may further suggest that the wild populations between 91 and 168 days (3 to 5 months). from Balboa, Coco Solo, Galveston, and San Juan are exceptionally similar in genotype, and different from Volume (Relative) of Feces Produced between F 1 to F 2 the St. Teresa control. There appears to be no meaning- This measurement, determined by setting volume ful correlation between this measure and geographic in a calibrated micropipette, indicates the health of distribution or latitude. the F~ generation in terms of burrow excavation and feeding by an unknown number of F~ specimens. The Initial Number of P1 • Pc Cross F~ died out in the Chatham • St. Teresa cross. The In each instance, a total of 20 isopods was used to measurement is a function of the days required for F~ commence the experiment. Ten males from the test production and is, therefore, better expressed in terms locality (P1) were crossed with i0 females from the of rate. Obviously this measure is also a function of control site at Saint Teresa, Florida (P,). In order to F 1 growth. avoid F 1 x P1 or F 1 • P~ backeross, these 20 adults were sacrificed shortly after the appearance of the Rate of Feces Production per Day F 1 generation. The cumulative feces produced by the F 1 generation per day was determined in order to reduce this meas- Number of Resultant F~ ure to a common denominator. This measure ranges The number of the resultant F 2 was determined by counting all young produced by the F 1 • F 1 No. Experiment Fz Rate mating. of feces production/day/F 1 Population Growth (%) 5 Norfolk, Virginia 0.03 Population growth was taken as a measure of 6 Beaufort, N. Carolina 0.06 population vigor. It was determined by dividing the 9 Balboa, Canal Zone 0.09 initial population size of 20 by the average size of the 8 Coco Solo, Canal Zone 0.09 [ Less than control iv2 population • t00. Gro~dh significantly in excess ~t Galveston, Texas 0.09 10 San Juan, Puerto Rico 0.09 of that of the control was considered to represent vigor Y Control 0.20 (+) and genetic compatibility; that genetically very 2 Savannah, Georgia 0.2t Equal to control similar to the control was considered to show an t2 San Francisco, California 0.41 absence of vigor (0). Zero growth ( -- ) suggests genetic 3 Charleston, S. California 0.83 Hybrid vigor incompatibility. The data are plotted on Fig. 3, where Vol. 17, 1Vo. 2, 1972 R.J. Menzies: Experimental Interbreeding in Limnoria t57

the three probably different cases are shown. It is Eltringham, S. K.: The effect of salinity upon the boring evident that the crossings with populations nearest activity and survival of Limnoria (Isopoda). J. mar. Biol. Ass. U.K. 41, 785--797 (1961 a). the Saint Teresa control (mean distance 1598 kin) -- Wood-boring activity of Limnoria (Isopoda) in relation show higher vigor than the control, whereas those to oxygen tension. Nature; Lond. 190 (4775), 512--513 most distant (mean distance 3408 km) from the St. (1961 b). Teresa control are more similar to the control in popu- --The respiration of Limnoria (Isopoda) in relation to salinity. J. mar. Biol. Ass. U.K. 45, 145--t52 (1965). lation growth and, hence, in genotype as measured by -- and A. R. Hockley: Migration and reproduction of the this means. wood-boring isopod Limnoria in Southampton Water. Limnol. Oceanogr. 6, 467--482 (t961). SHmmal'y Esakova, S. E. : Systematic position of Limnoria (Crustacea, Isopoda) from the Soviet coasts of the Black Sea. Zool. L Geographically disjunet populations of Limno- Zh. 44, 456--458 (1965). ria may be cultivated in the laboratory. Jones, L. T. : The geographical and vertical distribution of 2. The generation time for Limnoria tripunctata British Limnoria (Crustacea Isopoda). J. mar. Biol. Ass. U.K. 43, 589--603 (1963). Menzies is between 3 and 5 months. Kussakin, 0. G. : Some data on the systematics of the family 3. Limnoria tubervulata appears to be a valid Limnoriidae (Isopoda) from the northern and far-eastern species, closely related to Limnoria tripunctata. They seas of the U.S.S.R. Crnstaceana 5, 281--292 (t963). do pair in burrows bat produce non-viable young. Menzies, R. J. : A new species ofLimnoria (Crustacea: Isopoda) from Southern California. Bull. Sth. Calif. Acad. Sci. 50, 4. The presence of two closely related species in 86--88 (t951). the colder parts of the range of L. tripunctata -- The comparative biology of reproduction in the woodboring suggests the yet untested hypothesis that evolution isopod ernstacea, Limnoria. Bull. Mus. comp. Zool. Harv. proceeds most rapidly near the coldest limits of the 112, 364---388 (1954). -- The marine borer family Limnoriidae (Crnstacea, Isopoda). species. Apparently, populations of L. tuberculata at Part I Northern and Central America: systematics distri- the northern latitudinal limits (Chatham, Massachu- bution, and ecology. Bull. mar. Sci. Gulf Caribb. 7, t00-- setts) will interbreed with L. tripunctata from Saint 200 (1957). Teresa, Florida and Beaufort, North Carolina, but an -- The distribution of wood-boring Limnoria in California. Prec. Calif. Acad. Sci. 29, 267--272 (1958). P2 can not be produced, as the few _F1 produced in this --The identification and distribution of the species of instance die out. Limnoria. In: Marine boring and fouling organisms, 5. Populations closest to the control site show the pp 10---33. Ed. by D. L. Ray. Washington: University highest population growth or vigor, whereas those Press 1959. --Transport of marine life between oceans through the most distant are the same as, or very similar to the Panama Canal. Nature, Lend. 220 (5t69), 802--803 (1968). populations from the control site in population growth --, J. Mohr and C. M. Wakeman: The seasonal settlement of or vigor. wood-borers in Los Angeles-Long Beach Harbors. Wasmann J. Biol. 21, 47--119 (1963). Literature Cited Author's address: Dr. R. J. Menzies Beckman, C. and R. Menzies: The relationship of reproductive Oceanography Department temperature and the geographical range of the marine Florida State University wood borer Limnoria tripunctata. Biol. Bull. mar. biol. Tallahassee, Florida 32306 Lab., Woods Hole 118, 9--16 (t960). USA

Date of final manuscript acceptance: July t4, 1972. Communicated by J. Bunt, Miami

21 lV[arineBiology, Vol. 17