Change in Setal Pattern during Early Development of Eupolymnia Nebulosa (Polychaeta: Terebellidae) Grown in Simulated Natural Conditions

Eupolymnia nebulosa (Montagu) is a tubicolous worm with its body divided into two regions: thorax with biramous segments and three pairs of gills; abdomen with numerous segments lacking notopodia. The head bears grooved foodgathering tentacles which are not retractile into the mouth. The worm, a typical deposit feeder, lives in mucous tubes encrusted with sand. Although the family Terebellidae is homogeneous in terms of body organization and feeding ecology, there is a remarkable heterogeneity of developmental pattern. In the genera Lanice and Loimia, the life-cycle involves two pelagic stages separated by a short benthic larval stage; in other genera the development is mixed or direct (Bhaud et al. 1987; Pechenik, 1979; Caswell, 1981). It is important to study the development of representatives of the family which may reveal the adaptive significance of the different modes of development or may yield information about evolutionary relationships within the family. In several previous papers larval development (Bhaud & Grémare, 1988 a, b) and reproductive biology (Bhaud et al. 1987) of E. nebulosa have been reported from the Mediterranean coast. The present article reports observations on juvenile growth and morphological organization in natural conditions. This is the first step to growth rate studies in terms of temperature and food supply (Bhaud, 1988).

Download Full-text

Fragmentation modes and the evolution of life cycles

10.1101/120097 ◽

2017 ◽

Cited By ~ 1

Author(s):

Yuriy Pichugin ◽

Jorge Peña ◽

Paul B. Rainey ◽

Arne Traulsen

Keyword(s):

Growth Rate ◽

Life Cycle ◽

Population Growth ◽

Population Growth Rate ◽

Single Cells ◽

Adaptive Significance ◽

Life Cycles ◽

Mode Of Reproduction ◽

Size Groups ◽

Multicellular Organisms

AbstractReproduction is a defining feature of living systems. To reproduce, aggregates of biological units (e.g., multicellular organisms or colonial bacteria) must fragment into smaller parts. Fragmentation modes in nature range from binary fission in bacteria to collective-level fragmentation and the production of unicellular propagules in multicellular organisms. Despite this apparent ubiquity, the adaptive significance of fragmentation modes has received little attention. Here, we develop a model in which groups arise from the division of single cells that do not separate but stay together until the moment of group fragmentation. We allow for all possible fragmentation patterns and calculate the population growth rate of each associated life cycle. Fragmentation modes that maximise growth rate comprise a restrictive set of patterns that include production of unicellular propagules and division into two similar size groups. Life cycles marked by single-cell bottlenecks maximise population growth rate under a wide range of conditions. This surprising result offers a new evolutionary explanation for the widespread occurrence of this mode of reproduction. All in all, our model provides a framework for exploring the adaptive significance of fragmentation modes and their associated life cycles.Author SummaryMode of reproduction is a defining trait of all organisms, including colonial bacteria and multicellular organisms. To produce offspring, aggregates must fragment by splitting into two or more groups. The particular way that a given group fragments defines the life cycle of the organism. For instance, insect colonies can reproduce by splitting or by producing individuals that found new colonies. Similarly, some colonial bacteria propagate by fission or by releasing single cells, while others split in highly sophisticated ways; in multicellular organisms reproduction typically proceeds via a single cell bottleneck phase. The space of possibilities for fragmentation is so vast that an exhaustive analysis seems daunting. Focusing on fragmentation modes of a simple kind we parametrise all possible modes of group fragmentation and identify those modes leading to the fastest population growth rate. Two kinds of life cycle dominate: one involving division into two equal size groups, and the other involving production of a unicellular propagule. The prevalence of these life cycles in nature is consistent with our null model and suggests that benefits accruing from population growth rate alone may have shaped the evolution of fragmentation mode.

Download Full-text

Aspects of in vivo growth of the plerocercoid stage of Schistocephalus solidus

Parasitology ◽

10.1017/s0031182000046369 ◽

1973 ◽

Vol 67 (2) ◽

pp. 133-141 ◽

Cited By ~ 11

Author(s):

R. H. Meakins ◽

M. Walkey

Keyword(s):

Growth Rate ◽

Life Cycle ◽

Body Cavity ◽

Parasite Growth ◽

The Body ◽

Natural Conditions ◽

Schistocephalus Solidus ◽

Surgical Implantation ◽

In Vivo Growth

1. The in vivo growth of Schistocephalus solidus plerocercoids was investigated by surgical implantation of worms into the body cavity of uninfected, recipient sticklebacks. 2. Burdens of one, two and five worms were used. 3. Results show a reduction in parasite growth with both increasing size and increasing numbers of parasites. 4. Reasons for the decrease in growth rate of multiple burdens are discussed and reference is made to the significance of burden size in completion of the life-cycle under natural conditions.

Download Full-text

The larval structures and bionomics of Idgia iriomoteana (Coleoptera: Prionoceridae)

Acta Entomologica Musei Nationalis Pragae ◽

10.37520/aemnp.2021.023 ◽

2021 ◽

pp. 427-434

Author(s):

Makoto Asano

Keyword(s):

Life Cycle ◽

Larval Instar ◽

Instar Larva ◽

Adaptive Significance ◽

Winter Dormancy ◽

First Instar ◽

Complete Life Cycle ◽

The Family ◽

In Captivity

The life cycle, bionomics and mature larval structures of the Japanese prionocerid species, Idgia iriomoteana Nakane, 1980 were investigated in captivity. The results showed that I. iriomoteana has the following characteristics: (1) the larval morph is less advanced in terms of miniaturization, and larvae pass seven larval molts before they pupate; (2) the life cycle is univoltine with summer, not winter, dormancy; (3) the first instar larvae are larger than the size of the egg, but foetomorphic larval instar (which is observed in the Melyridae: Malachiinae) is not shown. Based on comparison with melyrid species, the degree of miniaturization, dormancy behaviour, adaptation to the tropical and subtropical climates and the adaptive significance of a large first instar larva are all discussed. This study is the first to report the complete life cycle of a member of the family Prionoceridae.

Download Full-text