J. Limnol., 62(1): 35-40, 2003 Adaptive strategies in populations of Chirocephalus diaphanus (Crustacea, Anostraca) from temporary waters in the Reatine Apennines (Central Italy) Graziella MURA*, Giovanni FANCELLO and Secondina DI GIUSEPPE Dipartimento di Biologia Animale e dell'Uomo, Università "La Sapienza", Viale dell'Università 32, 00185 Roma, Italy *e-mail corresponding author:[email protected] ABSTRACT To investigate the relationship between the adaptive strategies of Chirocephalus diaphanus (Crustacea, Anostraca) and the envi- ronmental characteristics of its habitat, we studied two populations living in high-altitude biotopes with very different characteris- tics, i.e. a semipermanent pool (Tilia Lake) and a temporary one (Illica Plain Pool), and we examined the essential features of their biological cycles (growth rate, reproductive biology, sex ratio and life cycle). The results show that the two populations adjust to the biotopes in which they live, fully exploiting the brief period available for development, in agreement with hypotheses formulated in studies of other colonizers of temporary environments. The strategy adopted by the Chirocephalus diaphanus population of Tilia Lake, a predictable and relatively constant environment, is similar to the k type, characterized by slow growth, late reproduction and a long life cycle. In contrast, the Illica Plain population presents rapid growth, precocious reproduction and a short life cycle, since it is highly dependent on the precariousness and unpredictability of the pool in which it lives. Key words: Anostraca, Chirocephalus diaphanus, life history, temporary waters, environmetal diversity, adaptive strategies perature range in which it normally lives is very wide 1. INTRODUCTION (5-26 °C) (Nourisson 1964), and there are occasional The life cycle of organisms, in its phenotypic ex- records of it in pools covered by a thick layer of ice pressions, represents a series of selective compromises (Hall 1961) or at temperatures above 30 °C (Mura imposed by different environmental variables. Natural 1991). Depending on the altitude of the colonized selection will modify the characteristics of the life cycle biotope, the biological cycle of different populations can to produce an adaptive strategy that optimizes individ- be autumn-winter, with a summer stasis due to disap- ual fitness and synthesizes the compromise between the pearance of the water, or spring-summer with a winter various selective pressures (Wilbur et al. 1974). The stasis due to freezing. Except for sporadic cases, Chiro- strategies adopted by populations of a species are re- cephalus diaphanus usually has a univoltine cycle lated to the population density-trophic resources rela- (Cottarelli 1966). tionship (Pianka 1970; Gadgil & Solbrig 1972), to stress from predatory pressure and competition (Hamer & 1.2. The study sites Appleton 1991), and to the duration of the colonized Tilia Lake (1591 m a.s.l.) is a semipermanent high- biotope (Marcus & Weeks 1997). pasture pool on Mount Tilia (1775 m a.s.l.) near To evaluate the importance of the duration and sta- Leonessa (Rieti) (Cottarelli 1966). The pool, with a bility of the biotope in anostracan crustaceans typically maximum depth of 97 cm, has a roughly rectangular confined to temporary water bodies, we chose two shape (54 × 48 m). Its total surface area is 2592 m2 and populations of Chirocephalus diaphanus living in its estimated volume is 474.3 m3. The water cycle be- biotopes with different environmental characteristics. gins with the melting of the snow, normally between The two pools are in the central Apennines north of March and April, followed by a variable period in which Rome in an area with winter snowfalls and dry sum- the water level oscillates depending on the temperature mers, and they both present a spring-summer cycle. and precipitation. However, the pool rarely dries up However, although at roughly the same altitude and thus completely. exposed to the same photoperiod and similar thermal Illica Plain Pool (1485 m a.s.l.) on Mount Inver- regime, they differ in the predictability and stability of saturo in the Laga Mountains is a small, oblong tempo- their water phase rary water body (25 × 16 m). It has a surface area of 264 m2, a maximum depth of 50 cm and a volume of 87.8 1.1. The species m3. This pool also has a spring-summer cycle. However, Chirocephalus diaphanus Prévost 1803 is the most because of its morphological and geological character- diffuse and tolerant species of the genus in Italy. For istics, it is characterized by erratic, short-term filling this reason, it is able to colonize temporary environ- and it often dries up before the animals can reach repro- ments both at sea level and at high altitude. The tem- ductive age. 36 G. Mura et al. 300 200 300 200 250 250 150 150 200 200 mm 150 100 150 100 cm cm mm 100 100 50 50 50 50 0 0 0 0 jul jul jun jan jan feb oct oct feb apr jun apr aug sep sep dec mar nov dec aug mar nov may may abrain snow rain snow 35 35 30 30 25 25 20 20 °C 15 °C 15 10 10 5 5 0 0 6/5 5/6 5/7 4/8 3/9 4/5 7/6 5/8 21/4 21/5 20/6 20/7 19/8 18/9 3/10 2/11 2/12 13/5 20/5 29/5 17/6 27/6 17/7 20/7 29/7 12/8 19/8 2/12 18/10 17/11 c 12/10 24/10 d air temp. (°C) air temp. (°C) 25 25 20 20 15 15 °C 10 °C 10 5 5 0 0 1/5 9/8 8/9 1/5 9/8 8/9 11/5 21/5 31/5 10/6 20/6 30/6 10/7 20/7 30/7 19/8 29/8 18/9 28/9 e 11/5 21/5 31/5 10/6 20/6 30/6 10/7 20/7 30/7 19/8 29/8 18/9 28/9 f water temp. water temp. Fig. 1. Seasonal variations of air and water temperature and precipitations during 2000 at Tilia Lake (a, c, e) and Illica Pool pool (b, d, f). laid in order to estimate the mean brood size in relation 2. METHODS to the increasing size of the animals. All the data for the two biotopes were analyzed statistically (STATISTICA Between April and August 2000, the two biotopes '98 for Windows, STATSOFT Inc®) to reveal any sig- were monitored on a weekly basis to evaluate the fluc- nificant differences. tuations of environmental conditions and to record in- formation about the basic characteristics of the life cycle 3. RESULTS of the animals. The abiotic environment was characterized by ob- 3.1. Characteristics of the biotopes servation of the climatic pattern and measurement of the Tilia Lake. The water-phase began on April 21st and the main chemical and physical variables (water tempera- water level remained constant until mid-May. Then ture, pH, electrical conductivity, total dissolved solids, there was a phase of constant decline due to evaporation surface area and volume of the pools). Particular atten- and lack of precipitation. In July, unusual rainfall tion was given to the oscillations of water temperature, caused the water level to rise again, but there was a sub- in view of its strong influence on the life of aquatic or- sequent decline until the beginning of autumn, when ganisms (Lake 1969). For this purpose, we installed a new rainfall led to full capacity of the pool. continuous measurement probe in the two pools, which Illica Plain pool. The water-phase began on May 3rd allowed a detailed analysis of the temperature excur- and there were alternate phases of decline and filling of sions throughout the water cycle. the pool until it dried completely on August 19th. The The biological cycles of the two populations were pool then filled again but did not reach full capacity. A examined by periodic sampling, which provided infor- phase of decline began on October 1st and lasted for 20 mation about the growth rate of the animals, their rate of days, after which rainfall again filled the pool to its differentiation and sexual maturation, and the sex ratio. maximum volume. The material sampled on each visit was divided by de- The statistical comparison of the climatic data velopmental stage and measured with a micrometric showed that the two biotopes had a very similar weather eyepiece mounted on a stereomicroscope. When the du- pattern (rainfall, snowfall, air temperature) (Figs 1 a-f) ration of the cycle permitted it, we also collected data in the study year (2000); in fact, there were no signifi- on the fertility of the two populations: we isolated the cant differences between the two areas (ANCOVA, P females of each sample and counted the number of cysts >0.05). Adaptive strategies in populations of Chirocephalus diaphanus 37 350 10 350 10 300 300 8 8 250 250 200 6 200 6 -1 -1 150 4 150 4 mg l 100 mg l 100 2 2 50 50 0 0 0 0 b a 21/4 4/5 20/5 8/6 27/6 29/7 23/9 2/12 4/5 20/5 7/6 27/6 20/7 5/8 12/10 2/12 TDS pH TDS pH 700 0.35 700 0.35 600 0.3 600 0.3 500 0.25 500 0.25 400 0.2 -1 400 -1 0.2 300 0.15 ppm 300 0.15 ppm 200 0.1 S cm 200 0.1 S cm 100 0.05 µ µ 100 0.05 0 0 0 0 21/4 4/5 20/5 8/6 27/6 29/7 23/9 2/12 4/5 20/5 7/6 27/6 20/7 5/8 12/10 2/12 d c conductivity salinity(ppm) conductivity salinity(ppm) 20 20 15 15 10 10 5 5 0 0 f e 21/4 4/5 20/5 8/6 27/6 29/7 23/9 2/12 4/5 20/5 7/6 27/6 20/7 5/8 14/8 12/10 2/12 s/v s/v Fig.