REPRODUCTION AND REPRODUCTIVE PERIODICITIES OF SOUTH FLORIDIAN LITTORINIDAE
(GASTROPODA: PROSOBRANCHIA) 1
THOMAS V. BORKOWSKF University of Miami, Rosenstiel School of Marine and Atlllospheric Science
ABSTRACT The planktonic egg capsules of several Floridian littorinids and the nurse- cells to which functional sperm attach during storage and copulatory transfer are illustrated. The position of sperm attachment to the nurse-cell may be of taxonomic importance. Some individuals of Littorina lineata, L. lineolata, Nodilittorina tuber- cuiata, and probably L. angulifera, had ripe eggs or sperm in every month of the year. The majority of animals of these species, however, and of L. ziczac, Tectarius muricatus, and Echininus nodulosus, were spent be- tween December and April. Spawning was related to seasonal critical temperatures, height of the species on the shore, and to tidal wetting. Spawning was periodic, ap- proximately lunar, or semilunar, and occurred whenever actual tidal levels exceeded mean high-water spring-tide levels (MHWS) during the spawning season. A diurnal rhythm was seen, even in the laboratory, as egg capsules were released only at the time of high tide in the field. Individual females released from 12,000 to 44,000 egg capsules in a season, depending on the species.
INTRODUCTION This is the first of a series of papers on the reproduction, growth, mor- tality, productivity, distribution, and zonational dynamics of some south Floridian Littorinidae. The series is based, in part, on a dissertation submitted to the University of Miami, Coral Gables, Florida. Thanks are due to Dr. Hilary B. Moore and Dr. Harding B. Owre for critically reviewing the manuscript. I am grateful also to the National Water Quality Administration for support by grant number WP-01433 to Dr. Moore. The species studied were Tectarius muricatus (L., 1758), Nodilittorina tuberculata (Menke, 1828), Echininus nodulosus (Pfeiffer, 1839), Lit- torina lineata Orb., 1841, Littorina lineolata Orb., 1840, Littorina ziczac (Gmelin, 1791). The three species Littorina lineata, L. lineolata, and L. ziczac belong to the Littorina ziczac species complex. Bequaert (1943) included all three species under one name, Littorina ziczac; Abbott (1964, 1968) split the
] Contribution No. 1411 from the University of Miami, Rosenstiel School of Marine and Atmospheric Science. "Permanent address; 8 Banyan St., Hobe Sound, Florida 33455. 1971] Borkowski: Reproduction of Littorinidae 827 L1TTORINA LINEOLATA A o .022MM X-SECTION
LITTORINA TECTARIUS LINEOLATA MURICATUS B c
FIGURE 1. Nurse-cells of Miami Littorinidae and the orientation of the sperm to these nurse-cells: A, nurse-cells of Littorina lineo/ata; B, mode of orientation for L. lineo/ata; C, mode of orientation for Tectarius muricatus. group into two, and finally three species. Borkowski & Borkowski (1969) firmly established the existence of three species by morphometric techniques, but changed the names slightly from those of Abbott (1968). Dr. Abbott (personal communication) has agreed with the present usage (Borkowski & Borkowski, 1969), but pointed out that the name L. lineata Orb., 184 I, is a homonym and must be replaced. The change is in preparation by Dr. Abbott. Most references to Littorina ziczac in the literature refer to the species complex as a whole and not to L. ziczac, sensu stricto. 828 Bulletin of Marine Science [21(4)
REPRODUCTION The reproductive anatomy of the northern Littorina littorea was thor- oughly described by Fretter & Graham (1962); Marcus & Marcus (l 963 ) described that of Littorina ziczac, sensu lato, L. angulifera, and L. {lava; Abbott (1954) examined that of Tectarius muricatus, Nodilittorina tuberculata, and Echininus nodulosus. Only minor differences from L. littorea were found. Copulation in all these species is followed by internal fertilization. The receptaculum seminis of the female stores and nourishes the sperm until they are used in fertilization. Transfer of the sperm to the female is aided by nurse cells (Fretter & Graham, 1962: 342) (Fig. 1). The coordinated beat of the sperm propels the sperm and nurse cell as a unit to the female. The eggs are fertilized as they pass the receptaculum seminis, are surrounded by fluid and a membrane in the albumen gland, and are invested with the outer covering in the capsule gland. Planktonic capsules are released by al1of the species studied (Fig. 2). The egg capsules of the Floridian species Littorina irrorata and L. meleagris are also illustrated here for comparison. Certain characteristics of the nurse cell may be of taxonomic importance. A large rodlike structure composed of normal sperm heads (Woodard, 1942) is found in the nurse cell of all of the tropical, or warm temperate, species so far studied, except L. nebulosa (Reinke, 1912). These include the six species in the present study, L. angulifera, L. irrorata (Woodard, 1942), and L. {lava (Marcus & Marcus, 1963). Species whose nurse cells lack the rod are L. nebulosa and L. saxatilis (Reinke, 1912), L. obtusata (Ankel, 1936), andL. neritoides (Battaglia, 19S2). The position of spermatozoan attachment to the nurse cell was found to differ among those littorinid species having nurse cells with rods. In Tectarius muricatus, Echininus nodulosus, L. {lava, and L. angulifera, the sperm were usually attached to the nurse cell at right angles to the rod, as shown in Figure 1,C, but many combinations of nurse cells and spermatozoa apparently lack specific orientation; for L. lineata, L. lineo/ata, L. ziczac, and Nodilittorina tuberculata, the attachment was invariably of the type shown for Littorina lineata in Figure I,B.
THE REPRODUCTIVE PATTERN Methods and Materials.-Animals used in the study of the reproductive pattern were obtained mostly from three areas, the natural arenaceous limestone platform called Jupiter Blowing Rocks (26°49'N, 8000S'W), the granite jetty at Government Cut (2so46'N, 80008'W), and the limestone rock seawall at the Bureau of Commercial Fisheries Tropical Atlantic Biological Laboratory (TABL) (2S044'N, 80010'W). Methods used included ash-free dry tissue weights taken twice-weekly 1971] Borkowski: Reproduction of Littorinidae 829
Gi
100
60 20
Echininus ~ 100160 nodulosus
20 ~ .~_, ....•....-.."'-~ .•.•....••'-4-...... , .•...... ••~ '-"~_._ W =':~""~~ Littorino
100 Littorino :~
100 LiUorino ~ 60 ZICZOC 20 1 -J -'-F-'-M A M J J A SON 0
FIGURE3. The seasonal variation of the percentage of ripeness of some south Floridian Littorinidae. at TABL (May-November 1969), monthly at Government Cut and Jupiter (August 1967-August 1969). In addition, twice-weekly collections were made at TABL for gonadal smears and to test the release of egg capsules in the laboratory (May-November 1969). Plankton tows were taken regularly at TABL at least twice a week at a high-water slack period or shortly after (January-November 1969). In preliminary tows, all capsules were in a very early stage of development. To obtain dry tissue weights, the shell was measured, then carefully 1971] Borkowski: Reproduction of Littorinidae 831
32.0
28.0 \ \ \ ...... •.... '•./ \ ...•." ....•....•..•'_. " ...' ..".. .~ 24.0 ...•...... f\\ .•.. ...•\. ,.•p' .••. / .. '.\ °c , ....•. • ',\ I ",\ I !! .'. .0.\ I ,, .: 20.0 ,. 'v.. I \ ,__.1 - = SI;A TEMPERATURES ',' ....• --- = MAXIMUM AIR TEMPERATURES .., 16.0 ...... = MINIMUM AIR TEMPERATURES . . ,~..... , \,
12.0 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
FIGURE 4. Ten-day means of sea temperatures at high water at the pier of the Rosenstiel School of Marine and Atmospheric Science, and maximum and minimum daily air temperatures at Miami International Airport for 1969. cracked with a hammer, and shell fragments were removed during examina- tion of the soft parts under a dissecting microscope. Tissues of females and males, separately, were dried in preweighed aluminum containers at 108°C for approximately 48 hours, then weighed on a torsion balance accurate to 2 mg. For the smaller animals « 10.0 mm), error was reduced by including several in each container. Plots of dry tissue weights against the height, cubed, which is an estimate of shell volume (Moore, 1936), were found to approximate a straight line. A standard size was chosen for each species; this was an estimated average size of the mature adults at Government Cut for the species of Littorina, and at TABL for Tectarius and Nodilittorina. The dry tissue weights for these standard sizes were then taken from the plots for each collection and plotted against time. The effect of change in shape of the shell on calcula- tions of standardization was examined and found to be negligible. Weights of the egg capsules were obtained by collecting 100 egg capsules from a single species, drying them in preweighed foil containers, and weighing each container on a torsion balance accurate to 10 micrograms. Gonadal smears were made regularly through the second half of 1967 and all of 1968 and 1969, and the percentage of ripe animals calculated. Spawning readiness was indicated when egg capsules were released in the laboratory by isolated animals. Plankton net tows near the field popula- tion at TABL showed the natural periods of release. 832 Bulletin of Marine Science [21(4)
TABLE 1
CRITICAL TEMPERATURE FOR THE ONSET OF SPAWNING IN SOUTH FLORIDIAN LITTORINIDS IN 1969
Temperatures (OC) Air Sea Date of Species* 1st spawn Mean Max. Min. High water Tectarius muricatus 31 June 69 27 30 23 30 Nodilittorina tuberculata 5 June 69 27 29 23 29 Littorina lineata 2 May 69 26 28 22 26 Littorina lineolata 7 April 69 25 27 20 25 Littorina ziczac 2 May 69 26 28 22 26 • Species arranged vertically as distributed on the shore.
An estimate of the number of egg capsules spawned per female in a season was obtained from laboratory experiments on egg-capsule release and differences in dry tissue weights from samples of the TABL population. The Seasonal Pattern.-The seven tropical western Atlantic littorinids studied so far, including Littorina angulifera (Lenderking, 1954), spawned in the warmer months of the year. Some animals of L. lineata, L. lineolata, Nodilittorina tuberculata, and probably L. angulifera, had ripe eggs or sperm in every month of the year (Fig. 3). The majority of the animals of these species, however, and of L. ziczac, Tectarius muricatus, and Echininus nodulosus, were spent between December and April. The gonads of all species filled with spawn in March and April as air and sea temperatures rose (Fig. 4), but the actual onset of spawning was delayed. For all species, the recorded period of pairing in apparent copula- tion and of plankton-tow captures of the planktonic egg capsules was shorter than the period during which most, or all, of the mature animals were ripe (Fig. 7). Table 1 indicates sea temperatures on the first date that the egg capsules of each species were collected in plankton tows in 1969. Since capsules of E. nodulosus were collected only twice, the species is not included in this table. The species in Table 1 are arranged in the approximate order of their distribution on the shore, and a progressively later onset of spawning can be seen upward on the shore. Littorina ziczac, the species lowest on the shore, reverses this trend and begins spawning at a later date than L. lineolala, above it. This delay for L. ziczac is also reflected in the percentage of spent animals from January through March. Lebour (1945) observed spawning in some of these species at Bermuda, but her observations were confined to the summer months. Lewis (1960) collected the planktonic egg capsules of T. muricalus off Barbados from 1971] Borkowski: Reproduction of Littorinidae 833
0.0.0.0.0.0. 120
Mg
80
40
~:L~J ~l~-::;y:!v/, 1 ~l~j MAY JUN JUL AUG SEP OCT NOV FIGURE 5. Tissue-weight fluctuations and plankton-tow collections of the egg capsules of five south Floridian littorinids in relation to the lunar period. From top to bottom: Tectarius muricatus, Nodilittorina tuherculata, Littorina lineata, L. lineolata, and L. ziczac. mid-June until August, but those of L. ziczac (s.l.) and N. tuberculata were found all year. If critical temperatures are involved, the lengthening of the spawning season of these latter species may be a result of the climate of Barbados. The seasonal mean air temperature of Barbados is about the same as that of Miami, but the seasonal range of temperature is less. Winter temperatures in Barbados seldom fall below 25°C. No correlations between the seasonal, and periodic, release of egg cap- sules and salinity, rainfall, wind, or wave action were found. 834 Bulletin of Marine Science [21(4)
0 cd UJ (;j 0 'tl >. > :J 0 tn Z .~ Q) 'tl 0 I- "0 .., > ~ •... ~ .., I 'fo :E ~ b ~ .; 'tl 'tl
Z 0 ~ tIl p:: . . . . ~ ~ en ~ If') "! en ~ ~ en ~ It) 0 "! ~ TiDE LEVEL (METERS) 1971] Borkowski: Reproduction of Littorinidae 835 Spawning Periodicity.-Several littorinids are known to show lunar, or semilunar, periodicity in spawning. These include Littorina angulifera (Lcnderking, 1954), L. neritoides (Lysaght, 1941), L. picta and L. pintado (Struhsaker, 1966), L. (lava (Marcus & Marcus, 1963), and possibly L. littorea (Tattersall, 1920; Thorson, 1946). To these we may now add the five species for which data are available here. Because littorinids which release planktonic egg capsules probably spawn only when partially or completely submerged, spawning is most likely to occur during the higher tides of the lunar cycle. The periodic fluctuation in tissue weight of five Floridian littorinids (Fig. 5) could be attributed to spawning because of the periodic presence of the planktonic egg capsules in plankton tows. Both were significantly correlated with the lunar cycle, but with a lag of 1 or 2 days. The relation between spawning and the tidal cycle for south Floridian littorinids and for L. neritoides (Lysaght, 1941), however, was only approximate. On the other hand, when actual tidal levels were substituted for predicted tidal levels (Fig. 6), spawning was found to occur in one or more of the Floridian littorinids whenever tidal levels rose above the mean high-water spring-tide level (MHWS) (Fig. 7). Littorinids apparently do not possess an endogenous lunar rhythm. Spawning became almost continuous in response to the very high tidal levels in the fall of the year of 1969, and, in the laboratory, egg capsules were released at every phase of the moon. It should be noted that in some years these fall tides may not occur, or may occur in the spring instead of the fall (Moore, personal communication). There is, however, at least a short-term memory for the time at which the tide will be highest. Spawning in the laboratory occurred only at the time of high tide in the field in Miami, in Hawaii (Struhsaker, 1966), and in northern Florida (Bingham, 1969). Spawning in the laboratory was induced by submergence or splashing. Changes in light cycle had no effect upon spawning time (Struhsaker, 1966) . Struhsaker and Bingham (1969) reported release of capsules both day and night, and no differences between daytime and nighttime plankton tows were noted in the present study. Tattersall (1920) reported that L. littorea released egg capsules mostly at night. Bingham (1969) found that a rise in temperature induced spawning in Littorina irrorata. Fecundity.-Examinations of female gonads revealed no depletion of egg supply between spawning episodes. Instead, the continuous reserve of eggs and the fact that the numbers of capsules released by some animals in the laboratory corresponded to observed drops in tissue weight in the field in- dicated that nearly 100 per cent of the females spawned at each opportunity. 836 Bulletin of Marine Science [21 (4) ..•...• 0 '"~ > 'u~ 0 P< Z '"•... ;:l ..•...•0 •... ..•...•0 ~ (J ~'" ;> 0 ~ "0 l:: '" '"~ c.!) ~ ~ '"P< 4( '"(,) OJ) • OJ)~ ~'""0 ..•...•.- 0.::•... ..J l::'" •••0 ~., o.~ '"8 >-l en ~ CD '0 en (,) ~ U) .9 z I W ~ d ..J ., 0 ~ 1<: U) c a. '" 4( 0.. () )- ~d ~ 4( ~ 2 ...~ ~ U) ~ ~ .I:J Z 'C ~ ~ ..J '"d ..J ~ (J 4( .9... 4( :ll: lE w S ~ ~ Z Z Z It: ~ 4( ~ •.. ~ 2 ..J a. •.. 0 ..J :J 4( 0 4( a. 1--= .J ..J U - en U) r...: ~ ~ ~ :I: :I: !ll: W 2 ::l 0 ~ 1971] Borkowski: Reproduction of Littorinidae 837 o 0 o o 0 o o q o - o 0 o o o 0 o 0 o o o 0 q 0 It") o If"l.q •.•• v-l N 00 It") It") •....• •....• •....• •....• •••• ' o o 0 o o o 0 o o 0 o o 0 o qq °If"l. qq v5 It") It") N•....• °- •••• \0 •....•~ •....• It") •....•r- 00 +- +- +- of- +- N o o 0 o o o o 0 o o 0" v:. It") 0'1 o ' •....• o•....• o•....• •....• •....•...• ...••....• o o ~ ~•....• ~ ~ •....•~ •....•r- •....• ai ai N•....• 00 •....• 838 Bulletin of Marine Science [21 (4) The fecundities of the rocky-shore species from Miami and Hawaii were quite similar (Table 2), especially if the seasonal totals of Miami littorinids are expanded to year-round totals. Differences are further reduced when amounts of spawn are standardized to an animal of common size. These are estimated fecundities, since the total output of a single littorinid cannot be known for certain. Tissue weights, as the basis of the estimates, are probably underestimates of spawn production. Some sources of error include the fact that tissue-weight collections may miss the spawning date entirely, a buildup in weight may be occurring in one part of the population as weight decreases in another part, or both buildup and decrease may be occurring at the same time. No relation between size of the animal and the number of capsules re- leased in the laboratory was found in the present study, by Struhsaker ( 1966), or by Bingham (1969). In each case, small animals released as many capsules as large animals, or more. Laboratory animals usually released only a fraction of the number indicated in this study for field populations. The fecundities (Table 2) will be related to the field populations in a later paper. SUMARIO REPRODUCCI6N Y PERIODICIDADES REPRODUCTIVAS DE LITTORINIDAE (GASTROPODA: PROSOBRANCHIA) EN EL SUR DE LA FLORIDA Se ilustran las capsulas de huevos planct6nicas de varios litorinidos flori- danos y las celulas-nodrizas a las cuales se adhiere el esperma funcional durante el almacenaje y traspaso copulatorio. La posici6n de la adherencia deLesperma a la celula-nodriza puede ser de importancia taxon6mica. Algunos individuos de Littorina lineata, L. lineolata, Nodilittorina tuber- culata y probablemente L. angulifera, tenlan huevos maduros 0 esperma en todos los meses del ano. Sin embargo, la mayorla de los animales de estas especies y de L. ziczac, Tectarius muricatus y Echininus nodulosus los gastaron entre diciembre y abril. EI desove estuvo relacionado con temperaturas cdticas estacionales, altura de las especies en la orilla y la acci6n humectante de la marea. El desove fue peri6dico, aproximadamente lunar 0 semilunar y tuvo lugar siempre que los niveles actuales de la marea excedieron la media del agua- alta de los niveles de la marea de primavera durante la epoca de desove. Un ritmo diurno se vi6 aun en ellaboratorio, ya que las capsulas de huevos eran liberadas s6lamente cuando habia mare a alta en el area. Hembras individuales liberaron de 12,000 a 44,000 capsulas de huevos en una estaci6n, dependiendo de la especie. 197 J] Borkowski: Reproduction of Littorinidae 839 LITERATURE CITED ABBOTT, R. T. 1954. Review of the Atlantic periwinkles, Nodilittorina, Echininus, and Tectarius. Proc. U.S. natn. Mus., 103: 449-464. 1964. Littorina ziczac Gmelin and L. lineo/ata Orbigny. Nautilus, 78: 65-66. 1968. Seashells of North America. Golden Press, New York, 280 pp. ANKEL, W. E. 1936. Prosobranchia. Tierwelt N.-u. Ostsee, 9(b1): 1-240. BATTAGLIA, B. 1952. Richerche sulla spermatogenesi atipica dei Gasteropodi Prosobranchi. II. Le cellule nutrici nella spermatogenesi di Littorina neritoides L. (Gasteropodo Prosobranco). Boll. Zool., 19: 195-201. BEQUAERT, J. C. 1943. The genus Littorina in the western Atlantic. Johnsonia, 1 (7): 1-28. BINGHAM, F. O. J 969. The influence of environmental stimuli on the direction of movement of the supralittoral gastropod Littorina irrorata, with notes on addi- tional biological aspects of the species. Master's Thesis, Florida State University, Tallahassee, Fla., 66 pp. BORKOWSKI, T. V. AND M. R. BORKOWSKI 1969. The Littorina ziczac species complex. Veliger, 11: 408-414. FRETTER, V. AND A. GRAHAM 1962. British prosobranch Molluscs: Their functional anatomy and ecology. Ray Society, London, 755 pp. LEBOUR, M. V. 1945. The eggs and larvae of some prosobranchs from Bermuda. Proc. zool. Soc. London, 114: 462-489. LENDER KING, R. E. 1954. Some recent observations on the biology of Littorina anguli/era Lam. of Biscayne and Virginia Keys, Florida. Bull. Mar. Sci. Gulf Carib., 3: 273-296. LEWIS, J. B. 1960. The fauna of rocky shores of Barbados, West Indies. Can. J. Zool., 38: 391-435. LYSAGHT, A. M. 1941. The biology and trematode parasites of the gastropod Littorina neritoides (L.) on the Plymouth breakwater. J. mar. biol. Ass. U.K., 25: 41-67. MARCUS, E. AND E. MARCUS 1963. Mesogastropoden von der Ki.iste Sao Paulos. Abh. math.-naturw. KI., 1963(1): 1-105. MOORE, H. B. 1936. The biology of Littorina littorea. I. Growth of the shell and tissues, spawning, length of life and mortality. J. mar. biol. Ass. U.K., 21: 721-742. REINKE, E. E. 1912. A preliminary account of the development of the apyrene spermato- zoa in Strom bus and of the nurse cells in Littorina. BioI. Bull. mar. bioI. Lab., Woods Hole, 22: 319-327. 840 Bulletin of Marine Science [21(4) STRUHSAKER, J. W. 1966. Breeding, spawning, spawning periodicity, and early development in the Hawaiian Littorina: L. pintado (Wood), L. pieta Philippi, and L. seabra (Linne). Proc. malac. Soc. Lond., 37: 137-166. TATTERSALL, W. ~. 1920. Notes on the breeding habits and life history of the periwinkle. Sci. Invest., Fish. Brch Ire., 1920(1): 1-11. THORSON, G. 1946. Reproduction and larval development of Danish marine bottom invertebrates. ~eddr Kommn Danm. Fisk.-og Havunders., Serie: Plankton, 4: 1-523. WOODARD, T. ~., JR. 1942. Development of the nurse-cells of Littorina irrorata (Say). Trans. Am. microsc. Soc., 61: 361-372.