Diapause egg production in Acartia (Paracartia) latisetosa (Crustacea, Copepoda, Calanoida)

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Diapause egg production in Acartia (Paracartia) latisetosa (Crustacea, Copepoda, Calanoida) Genuario Belmonte

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Dipartimento di Biologia , Università degli Studi , Lecce, Italy Published online: 28 Jan 2009.

To cite this article: Genuario Belmonte (1992) Diapause egg production in Acartia (Paracartia) latisetosa (Crustacea, Copepoda, Calanoida), Bolletino di zoologia, 59:4, 363-366, DOI: 10.1080/11250009209386694 To link to this article: http://dx.doi.org/10.1080/11250009209386694

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Boll. Zool. 59: 363-366 (1992)

Diapause egg production in Acartia (Paracartia) latisetosa (Crustacea, Copepoda, Calanoida) GENUARIO BELMONTE

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Dipartimento di Biologia, Università degli Studi, Lecce (Italy)

ABSTRACT The life-cycle of the abundant and frequent calanoid copepod Acartia (Paracartia) latisetosa is not completely known. Eggs of three morphological types and at least two biological meanings were obtained from adult specimens under laboratory conditions. Two types («smooth» and «brush-like») were subitaneous. A third, «spiny», type rested for at least 50 days before hatching and was considered diapausal. It was suggested that the production of these different types of eggs helps A. latisetosa to overcome periodic, or unpredictable, crises typical of the confined brackish environments where this species is abundant. This is the first record of a resting stage in A. latisetosa. KEY WORDS: Life-cycle - Resting-eggs - Acartia - Copepods. ACKNOWLEDGEMENTS I am very grateful to Prof. G. Colombo for encouragement, Dr. P. Trotta for algal cultures, and Dr. A. Ianora and Prof. F. Boero for helpful criticisms, this research was supported by grants of the Ministero dell'Università e della Ricerca Scientifica e Tecnológica (60% and 40% programmes). (Received 17 September 1991 - Accepted 28 March 1992)

INTRODUCTION

The calanoid copepod Acartia (Paracartia) latisetosa (Kriczaguin, 1873) has been found in many localities of the Mediterranean Sea (see, for instance, Steuer, 1929; Carli & Crisafi, 1983). The only extra-Mediterranean records are from Mauritania (Rose, 1933) and Madagascar (Dussart, 1989). Like most Acartiidae, A. latisetosa is restricted to coastal and brackish waters. In these environments the Acartiidae are abundant, sometimes being the dominant component of Zooplankton (Jeffries, 1964; Tranter & Abraham, 1971; Youngbluth, .1980; Castel & Courties, 1982). A. latisetosa inhabits these confined environments in congeneric associations (see, for instance, Comaschi-Scaramuzza, 1987; Belmonte et al., 1989; Lakkis & Zeidane, 1990). The high hydrological variability of the coastal brackish waters determines sharp density fluctuations of copepod populations. In many cases calanoids desappear from the plankton but are able to persist in the same area as resting stages in the sediments. This well known phenomenon among freshwater planktonic organisms occurs also among marine neritic plankters. Data on resting-eggs of marine calanoids have been available for more than 20 years (Sazhina, 1968), but recent records of resting stages in Calanoida suggest that. they could be more common than previously thought (Grice & Marcus, 1981). " All Acartia species with a known life-cycle can. produce resting eggs (for a list see Uye, 1985), and this feature might be typical of the genus. Some species of Acartia, such as A. erytbraea, have spiny resting-eggs, whereas other species, such as A. clausi, have smooth ones (Kasahara et al., 1974). Despite the abundance and frequency of A. latisetosa the only available details of its life-cycle are reported by Crisafi & Crescenti (1972), who described all instars of the copepodid stage. Eggs and nauplii have still to be described.

MATERIALS AND METHODS Acartia (Paracartia) latisetosa was reared in the laboratory under controlled conditions. Adults were sorted from Zooplankton samples taken from the Acquatina (40°26' lat. N; 18° 15' long. E) and Alimini (40° 12' lat. N; 18°27' long. E) brackish-water lakes (along the Italian southern Adriatic coast) from April to May 1990. In the laboratory, 65 adult females from natural habitats were cultured into 50 cm1 flasks with a density of 1 female/10 cm5. Water was collected at sampling site (salinity, 30-32%o), and filtered through a 50 um mesh size plankton net. Cultures were supplied with a mixture of Isochrysis sp. (Prymnesiophyta) together with Dunaliella sp. (Chlorophyta, Chlorophyceae), Tetraselmis sp. (Chlorophyta, Prasiniophyceae) and Monocbrysis sp. (Chrisophyta), as algal food with a final concentration of 2 x 107 cell/liter. All flasks were maintained at a constant temperature (19° C ± 1.0) under continuous illumination (L = 24 h) to favour phytoplankton growth. Flasks were examined daily, and laid eggs were isolated to

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observe their morphology. To minimize influences of laboratory conditions only 220 eggs laid the first day of rearing were utilzed to determine the hatching time. For observations with Scanning Electron Microscope (SEM), eggs were fixed with Glutaraldehyde (2.5%) and Paraformaldehyde (1%) in Na-Cacodilate buffer (0.2 M) and sea water (20%). They were rinsed in Na-Cacodilate buffer (0.2 M) containing sea water (20%) and Saccharose (6%), and successively post-fixed in OsO4. The dehydration was performed in increasing concentrations of Acetone (10, 30, 50, 75, 90, 100%) with eggs contained in plastic capsules capped with filter paper. These capsules were subjected to the critical point-drying procedure, and then eggs were sputtered with gold.

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RESULTS

Like other acartiids, Acartia (Paracartia) latisetosa does not produce ovisacs, and eggs are released free in the sea water. Mature females laid eggs of at least three morphological types as described below and summarized in Table I. The most common type of egg, here defined «smooth», had an external surface without evident ornamentation (Fig% 1A, B), and hatched 24-48 h after laying. At the light microscope, embryonic developmental stages can be recognized, from the two-blastomere stage to pre-hatching nauplius. Newly laid eggs were darker than pre-hatching eggs. The second egg type was «spiny»; it had branched echinaid projections on the chorion (Fig. IC, D), and hatched at least 50 days after deposition. The third egg type was spiny, but the spines were shorter than those of the second egg type and conferred a brush-like appearance to the egg surface (Fig. IE, F). SEM observation showed that also these short spines were branched. These eggs had a hatching time ranging from 24 to 48 h similar to that of smooth eggs. Females produced also smooth, unfertilized eggs that ' did not hatch. These eggs were first recorded from one isolated female without spermatophore and apron, that is a structure associated with spermatophore reception (Kriczaguin, 1873), and then from another female, isolated as C-IV (copepodid, fourth instar), which, after maturation, produced 29 unfertilized eggs in two days. These eggs were not considered in the present study.

DISCUSSION The eggs of Acartia (Paracartia) latisetosa are polymorphic, but it was not possible to assign differentreproductive meanings to all types. The «smooth» type is a suitaneous egg, whereas the «spiny» one undergoes an interruption in its development. This study proves the existence of a resting egg in the life-cycle of one of the most widespread calanoid species along the Mediterranean coasts. This type of egg probably represents a diapausal stage as a result of developmental conversion {sensu Smith-Gill, 1983) in the life cycle of A. latisetosa. This hypothesis is supported by the fact that spiny resting-eggs are morphologically different from smooth subitaneous ones. Furthermore, many resting, spiny-éggs were laid together with subitaneous, smooth ones. But even under the same experimental conditions they had a different fate, evidently because they were differently programmed. Because of the constant conditions under which this species was reared, and the season in which sampling of adults were carried out, these eggs could not be considered as «overwintering» stages, but simply as a way for the species to overcome unpredictable crises (possibly «crowding»), recorded in Mediterranean coastal bracksih waters also in the summer (Ceccherellieifl/., 1987). Spiny eggs have been described in the plankton and were identified as calanoid eggs (Steuer, 1910). Most marine calanoids are free egg-laying, without ovisacs (Sazhina, 1987). As a consequence, the time needed to complete embryonic development (within the egg) results in the sinking of the egg of some dozen metres from the point of laying, the distance depending on water viscosity, and weight and size of the egg. Eggs with modified surfaces (spiny, in our case) could obtain a larger supporting surface which retards the sinking and favours transport by sea currents. The latter possibility is increased if the egg persist in the water for a long time. A. latisetosa, however, is a neritic species and reaches high densities along the coasts or in confined, brackish water environments. The spiny egg of this species, laid in shallow and almost calm waters, has little chance for a large horizontal dispersal. In these environments, this

TABLE I - Percentages, dimensions, and hatching-time of three egg-types in the calanoid Acartia (Paracartia) latisetosa. Data obtained on 220 eggs laid in laboratory from 28 April to 2 May, 1990.

Egg type

No./lOO eggs

diameter (um ± SD)

Smooth Spiny Brush-like

41.25 31.25 27.08

65.2 s 1.5 67.5 ± 2.1 63.6 ± 1.6

spine length (urn ± SD)

10.9 ±2.1 3.6 ± 0.3

hatched eggs/24 h

days to hatching half egg number

67.8 0.0 68.5

.1 50 1

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EGGS OF ACARTIA LATISETOSA

Fig. 1 - Morphology of three main egg-types in Acartia (Paracartia) latisetosa. A, B: egg with smooth surface. C, D: spiny egg with long spines. E, F.- «brush-like» egg with short spines on the surface. A, C, E: Bar, 50 (xm; light microscope photographs. B, D, F: Bar, 10 um; SEM photographs.

type of egg inevitably sinks to the bottom. There the spiny surface could keep mud particles away from the egg surface, so avoiding damage by scratching or compression during the resting period. The abundance of resting eggs on bay sea-beds is well known (Kasahara et al., 1974; Lindley, 1990; Marcus, 1990) there they constitute a kind of «seed-bank» from which planktonic populations can be restored. In general, variations of environmental factors influence the presence of a planktonic population. The presence of A. latisetosa, or other species, in particular environments could be due, to different extents, to this «seedbank» in which the species overcomes unfavourable conditions.

In confined environments the resting stages may represent not only the possibility of overcoming adverse conditions, but also a way of increasing dispersal possibilities, like passive transport in the atmosphere (e.g., by aquatic birds). It is difficult to identify a functional meaning for the second type of spiny egg. Some recent indications confirm the existence of more than two types of eggs in calanoid copepods (Santella & Ianora, 1990); however it is impossible to explain why there are two morphologies for a subitaneous strategy. Deposition of unfertilized eggs may be due to an automatism that switches on with the last moult of the female, with or without the reception of male spermatophores.

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REFERENCES Belmonte G., Benassi G., Ferrari I., 1989 - L'associazione di 4 specie di Acartia nel lago di Acquatina (Basso Adriático). Oebalia, XV-1, N.S.: 519-522. Carli A., Crisafi P., 1983 - Copepodi lagunari. In: Guide per il riconoscimento delle specie animali delle acque lagunari e costiere italiane. 11. AQ/1/230, CNR, Roma, 125 pp. Castel J., Courties C., 1982 - Composition and differential distribution of Zooplankton in Arcachon bay. J. Plankton Res., 4: 417-433. Ceccherelli V. U., Gaiani V., Ferrari I., 1987 - Trophic state gradients and zooplankton and zoobenthos distribution in a Po river delta lagoon. Chemosphere, 16: 571-580. Comaschi-Scaramuzza A., 1987 - Studio di popolazioni di copepodi planctonici nel bacino settentrionale della Laguna di Venezia. 11. Giugno 1977 - Giugno 1978. Arch. Oceanogr. Limnol., 21: 1-17. Crisafi P., Crescenti M., 1972 - Comportamento, morfologia, sviluppo, misure, confronti e revisione di otto specie della famiglia Acartiidae, incontrate in acque marine inquinate soprattutto da scarichi industriali. Boll. Pesca Piscic. Idrobiol., 27: 221-254. Dussart B., 1989 - Crustacés Copépodes Calanoîdes des eaux interieures africaines. Crustaceana, Suppl. 15, 205 pp. Grice G. D., Marcus N. H., 1981 - Dormant eggs of marine copepods. Oceanogr. Mar. Biol. ann. Rev., 19 125-140. Jeffries H. P., 1964 - Comparative studies on estuarine Zooplankton. Limnol. Oceanogr., 9: 348-258. Kasahara S., Uye S., Onbe' T., 1974 - Calanoid copepod eggs in seabottom muds. Mar. Biol., 26: 167-171. Kriczaguin V., 1873 - Otchot o faunisticheskich issliedovanijah, proisviedionnih letom 1872 g. na vostochnom beregu chernogo morya. Zapiski kyevskogo obshiestva jestetvoispytatielei Kyev, 3: 415-417. Lakkis S., Zeidane R., 1990 - Associations congeneriques d'acartia (Copepoda, Calanoida) dans les eaux cotieres Libanaises: Calcul

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des indices d'«overlap» et de «niche hypervolume». Rapp. Comm. int. Mer Medit., 32: 223. Lindley J. A., 1990 - Distribution of overwintering calanoid copepod eggs in sea-bed sediments around Southern Britain. Mar. Biol., 104: 209-217. Marcus N. H., 1990 - Calanoid copepod, cladoceran, and rotifer eggs in sea-bottom sediments of northern Californian coastal waters: identification, occurrence and hatching. Mar. Biol., 105: 413-418. Rose M., 1933 - Faune de France. 26. Copepodes pelagiques. P. Lechevalier, Paris, 374 pp. Santella L., Ianora A., 1990 - Subitaneous and diapause eggs in Mediterranean populations of Ponteila mediterranea (Copepoda: Calanoida): a morphological study. Mar. Biol., 105: 83-90. Sazhina L. I., 1968 - O zimuyushchikh yaitsakh morskikh Calanoida. Zool. Zh., 47: 1554-1556. Sazhina L. I., 1987 - Rasmiozhenie, rost, produkciya morskikh veslonogikh racoobraznikh. Naukova Dumca, Kyev, 156 pp. Smith-Gill S. J., 1983 - Developmental plasticity: developmental conversion versus phenotypic modulation. Am. Zool., 23: 47-55. Steuer A., 1910 - Adriatische Planktoncopepoden. Sber. Acad. Wiss. Wien, mat.-nat. Kl., 119, Abt. 1: 1005-1039. Steuer A., 1929 - Die Arten der Copepodengattung Acartia in der mediterranen Provinz. Sber. Akad. Wiss. Wien, mat.-nat. Kl., 138, Abt. 1: 497-516. Tranter D.J., Abrahams., 1971 - Coexistence of species of Acartiidae (Copepoda) in the Cochin Backwater, a monsoonal estuarine lagoon. Mar. Biol., 11: 222-241. Uye S., 1985 - Resting egg production as a life history strategy of marine planktonic copepods. Bull. mar. Sci., 37: 440-449. Youngbluth M. J., 1980 - Daily, seasonal, and annual fluctuations among Zooplankton populations in an unpolluted tropical embayment. Estuar. coast. mar. Sci., 10: 265-287.